Minor fixes and enhancements.

* Add general purpose user write permission test function to base
  window class.
* Check user write permissions before saving project, schematic and
  library files.
* Remove displaying file dialog every time the project file is saved.
* Display absolute paths for non-root sheet file in title bar.
* Remove redundant command table entry from schematic editor.
* Remove unused variables to fix GCC 4.6 warnings.
* The usual Doxygen comment and coding style policy fixes.

* Disable save library command when user does not have permission to write
  the active library.
* Append the active library file name displayed in the title bar with read
  only when the user does not have write permission.
* Test the selected folder permissions when user chooses the save library
  as command.
* The obligatory coding style policy fixes.

Eeschema: optimize import of footprints names ( .stf files) that was time consumming with large designs.

eeschema: add SCH_SHEET_PIN_T in ParentItems collector, convert sch_collectors.* to native unix format

Eeschema: fix bug that crashes libedit (after creating a new pin, repeat it (insert key), delete the new repeated pin and try to repeat)

All: use double instead of int to store zoom values.

* Change the minimum required CMake version to 2.6.4 for all build platforms
  except Windows and OSX.
* Move all schematic plot code from plot.cpp into the appropriate schematic
  objects.
* Create SCH_SCREEN plot method to plot all objects in the schematic
  screen.
* Delete plot.cpp and remove it from the CMakeList file.

* Move code from function ClearProjectDrawList() into SCH_SCREEN object
  Clear() method.
* Delete eeschema/delsheet.cpp as none of the code in it is ever called.
* Move global spice and net list command line variables into SCH_EDIT_FRAME
  object as priviate members and provide access methods.
* Remove unnecessary header includes from eeschema/sheet.cpp.
* Minor coding policy fixes.

Pcbnew: fix a minor issue.
Version update.

Annotation of multiparts gets CHINAME compared. This fixes bug when annotating components of same value (model) in several forms (e.g. dual opamp in single-body and dedicated representation).

* Fix debug build warning (lp:793373).
* Changed sheet edit restore and undo to use object copy and replace method.
* Add minimum width and height constraints when resizing sheets that have
  hierarchical pins.
* Fix drag sheet hot key bug.
* Change Doxygen configuration to extract private methods and members
  when creating documentation.
* Fix a bunch of Doxygen comment warnings.

Try to fix bug 639683 : Illegal reference strings are now detected and replaced by default prefix for old schematics or rejected in schematic edition.

Eeschema: add direct acces to LibEdit in popup menu, when a component is selected ( Whishlist #788621 ). This new command calls Libedit and load the lib component corresponding to the selected schematic component.

Libedit: actual line thickness  taken in account by collector. Thick lines are now more easy to locate. Fix incorrect boundary box calculations for LIB_PIN items. Very minor other fixes.

* Add drag context menu entry for junctions that actually form a junction
  with wires to EESchema.
* Add function to test for junctions to SCH_COLLECTOR class.
* Create annotate type and sort order enums to eliminate magic numbers
  used in annotate code.
* Remove duplicate Doxygen comments from annotate.cpp and improve the
  actual Doxygen comments in wxEeschemaStruct.h.

Pcbnew: fix very minor issue.

* Remove most (not all) variables that were initialized but never used that
  cause GCC 4.6 to generate a warning.
* Fix bug in schematic library editor best zoom calculation.