Pcbnew: Add pcad2kicad pcb plugin, to import PCAD boards ( .pcb ASCII data file PCad 2000 format ) from Alexander Lunef

* Create new GEDA PCB plug in.
* Add support for opening GEDA PCB footprints with module editor.
* Make import footprint file dialog remember last selected footprint
  type during current session.
* Update module editor file import to use new GEDA PCB plug in.
* Let IO_MGR know about GEDA PCB plug in.
* Create a WHITESPACE_FILTER_READER to simplify parsing GEDA PCB footprint
  files.

Pcbnew: board editor: allows pad edition by hotkey 'E' (was accessible only by mouse button right click)
All: minor code cleaning and very minor bug fixes.

Because now there are 2 formats, board backup files extensions are .brd-bak or .kicad_pcb-bak instead of the old .000 extension, depending on the initial file format.

Pcbnew: fix bug:  missing call to SetFileFormatVersionAtLoad after loading a board, in legacy format.

fix a fairly serious bug which would leave SOLDERMASK_LAYER_FRONT layer turned off in PADs, when loading *.kicad_pcb files

Pcbnew: add a dialog to load a legacy file in "old" projects, when the .kicad_pcb file is not existing, and the correspoinding .brd file exists.
Fix also an issue in pcb_parser when a netclass name is just a number (like a track width as name)

fix pcbnew file save as problem, if previous file by same basename did not exist.  Show default file ext.

Add KiCadPcbFileExt global.

Pcbnew: Drc dialog: fix a old very minor bug.
Added: single click on an item in marker list moves the board  graphic cursor on the corresponding marker location on the board
Double clicking is not modified.

Also a minor cosmetic enhancement

Eeschema: Add hotkey 'U' to edit reference. Better filtering for  hotheys V, F, U: now the corresponding field is selected without selection list between component and the field.

Try to fix an unwanted left mouse release button event, when closing a dialog on a click or double click,
and therefore when the mouse butoon is released in the parent window
Minor other fixes.

Pcbnew: plot solder mask layer with min width value specified: algorithm modified to reduce artifacts.

Pcbnew: commit patch from Heikki Pulkkinen (via displayed with its right size and clearance during track creation/edition)

* 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.

Pcbvew: fix a strange bug which swap x and y values for pad offsets when reading a s expr *.kicad_pcb board file.

which can eliminate a subsequent call to READ_LINE::Line() for a small performance gain.