Fix some coverity warnings (not initialized members). Add comments. Better (more informative) title in dialog to download .pretty libs.

Gerbview: Add support for recent File Format Attribute metadata, both for X2 Gerber file format and X1 (R274X) format.
Pcbnew already uses this attribute when creating Gerber files.
Because Gerber files using this attribute identify the board layers stackup, Gerbview (if this attribute is defined) can sort gerber images stach up like the board.
(in layer manager, just right click to access to the sort menu)

  steps to better support devices with precise scrolling deltas (trackpads).
  Scrolling is done in the handler rather than creating and firing cmd events.
  This is intended to support two-finger scrolling on the Magic Trackpad.
- Added a preference, 'Use mousewheel to pan', to allow panning by default
  on mousewheel events.  This reverses the existing behavior where unmodified 
  mousewheel zooms and Shift/Cmd modified pans.  

  The old behavior was:
  - Unmodified scrollwheel performed zoom in/out
  - Shift modified scrollwheel performed pan up/down
  - Cmd modified scrollwheel performed pan left/right
  - Shift+Cmd modified scrollwheel performed zoom in/out
    with no cursor warp

  With the new preference checked, this changes to:

  - Unmodified scrollwheel performs pan up/down
  - Shift modified scrollwheel performs pan left/right
  - Cmd modified scrollwheel performs zoom in/out
  - Shift+Cmd modified scrollwheel performs zoom in/out
    with no cursor warp

  With the preference unchecked, this is now:
  - Unmodified scrollwheel performed zoom in/out
  - Shift modified scrollwheel performed pan left/right
  - Cmd modified scrollwheel performed pan up/down
  - Shift+Cmd modified scrollwheel performed zoom in/out
    with no cursor warp

  It should be noted that for the last case, the behavior has changed.
  This is not arbitrary.  This now matches expected behavior for an OS X
  application.  This also matches what wxWidgets expects on this platform
  as wxWidgets changes the axis of mousewheel events to horizontal when
  the event is shift-modified.

  The preference is added everwhere that mouse preferences previously
  existed, i.e., eeschema, pcbnew and gerbview.  The 3D Viewer does
  not yet honor this preference, but behaves as if it was checked.
  The pl_editor does not currently have any preferences to honor.

  As with the magnify event support, this covers canvases for all
  current tools, EDA_DRAW_PANEL, EDA_3D_CANVAS and EDA_DRAW_PANEL_GAL.

  This does NOT modify the behavior of mousewheel zooming, though it
  probably should.  This remains unsuitable for use with a trackpad,
  use pinch-to-zoom instead.

Better separation between Pcbnew code and Gerber code.
Update export to Pcb code (uses now the version 4  kicad_pcb file format).

Export to Pcbnew is broken, but it is a very rarely used feature. It will be fixed later.

2) Change from legacy Cu stack to counting down from top=(F_Cu or 0).
   The old Cu stack required knowing the count of Cu layers to make
   sense of the layer number when converting to many exported file types.
   The new Cu stack is more commonly used, although ours still gives
   B_Cu a fixed number.
3) Introduce class LSET and enum LAYER_ID.
4) Change *.kicad_pcb file format version to 4 from 3.
5) Change fixed names Inner1_Cu-Inner14_Cu to In1_Cu-In30_Cu and their
   meanings are typically flipped.
6) Moved the #define LAYER_N_* stuff into legacy_plugin.cpp where they
   can die a quiet death, and switch to enum LAYER_ID symbols throughout.
7) Removed the LEGACY_PLUGIN::Save() and FootprintSave() functions.
   You will need to convert to the format immediately, *.kicad_pcb and
   *.kicad_mod (=pretty) since legacy format was never going to know
   about 32 Cu layers and additional technical layers and the reversed Cu
   stack.

!   The initial testing of this commit should be done using a Debug build so that
    all the wxASSERT()s are enabled.  Also, be sure and keep enabled the
    USE_KIWAY_DLLs option.  The tree won't likely build without it.  Turning it
    off is senseless anyways.  If you want stable code, go back to a prior version,
    the one tagged with "stable".

*   Relocate all functionality out of the wxApp derivative into more finely
    targeted purposes:
    a) DLL/DSO specific
    b) PROJECT specific
    c) EXE or process specific
    d) configuration file specific data
    e) configuration file manipulations functions.

    All of this functionality was blended into an extremely large wxApp derivative
    and that was incompatible with the desire to support multiple concurrently
    loaded DLL/DSO's ("KIFACE")s and multiple concurrently open projects.
    An amazing amount of organization come from simply sorting each bit of
    functionality into the proper box.

*   Switch to wxConfigBase from wxConfig everywhere except instantiation.
*   Add classes KIWAY, KIFACE, KIFACE_I, SEARCH_STACK, PGM_BASE, PGM_KICAD,
    PGM_SINGLE_TOP,
*   Remove "Return" prefix on many function names.
*   Remove obvious comments from CMakeLists.txt files, and from else() and endif()s.
*   Fix building boost for use in a DSO on linux.
*   Remove some of the assumptions in the CMakeLists.txt files that windows had
    to be the host platform when building windows binaries.
*   Reduce the number of wxStrings being constructed at program load time via
    static construction.
*   Pass wxConfigBase* to all SaveSettings() and LoadSettings() functions so that
    these functions are useful even when the wxConfigBase comes from another
    source, as is the case in the KICAD_MANAGER_FRAME.
*   Move the setting of the KIPRJMOD environment variable into class PROJECT,
    so that it can be moved into a project variable soon, and out of FP_LIB_TABLE.
*   Add the KIWAY_PLAYER which is associated with a particular PROJECT, and all
    its child wxFrames and wxDialogs now have a Kiway() member function which
    returns a KIWAY& that that window tree branch is in support of.  This is like
    wxWindows DNA in that child windows get this member with proper value at time
    of construction.
*   Anticipate some of the needs for milestones B) and C) and make code
    adjustments now in an effort to reduce work in those milestones.
*   No testing has been done for python scripting, since milestone C) has that
    being largely reworked and re-thought-out.

Eeschema: better name for m_SheetList (changed to m_SheetPath) member of  class NETLIST_OBJECT.

   File "rules" has instructional text as comments near top.

2) Convert all text files in repo to LF line ending form.
   Any checkout done with "rules" in play will convert the working
   tree to native line ending, while keeping repo as LF line ending.

Fixed layer picker for exporting to pcbnew
Realigned pcb layer name with class BOARD

More layer classification cleanup

Implemented the LAYER_NUM typedef (LAYER was already taken as a class name...) to represent a layer number.

- Renamed ReturnMaskLayer to GetLayerMask (since it's a plain getter)

added option to allow zooming around the crosshair instead of the center; can be enabled via options or by holding alt while using the mousewheel

* Fix offset errors when scale factor greater is than one.
* Changed behavior of fit in page when not drawing border and
  title block to fit board outline in page.
* Fix offset errors when mirroring (still not 100% correct on MSW with
  wxWidgets 2.9.4).
* Lots of the usual code cleaning and simplifying.

Pcbnew: automatic selection of plugin when loading a file with .kicad_pcb extension from history list.
Very minor other fixes

Should allow Pcbnew code easier to change and Gerbview code more understandable and easier to maintain.
Code cleaning (remove dead code, add comments).
Minor other enhancements.

If enable in preference menu, allow the pan with drag mouse with middle button down.
both unlimited and limited pan is allowed.

Pcbnew: Hight contrast mode: commit last patch from Miguel Angel Ajo Pelayo, which also  fixes an old bug.
All: prepare better compatibility with wxWidgets 2.9.4. Works fine with 2.8.x (I hope...)

* EDA_DRAW_FRAME completely encapsulated.
* Encapsulate the the low hanging fruit in EDA_DRAW_PANEL.