improvements to python's GIL acquisition and release, but not done yet, since I think the GIL needs to be acquired even when not involving wxPython.

Pcbnew: fix issues:   Ensure pads type connector  have a drill size= 0, like SMD pads. Ensure keepout zones have no net.

Pcbnew: Partial merge from pcad2kicad (from Alexander Lunev). Fix an old bug related to pads with offset: sometimes the connection to a zone was not detected.

* Fix all Doxygen warnings except polygon files.
* Add footprint library table tasks to TODO.txt.
* Add definition to drag.h to prevent nesting.
* Coding policy fixes.

Pcbnew: fix Bug #1148785 (pcbnew crashes when using only one layer in autorouter ) , and a minor bug in dialog cleanup.

Still fix minor issues in dialog_edit_module_for_BoardEditor.cpp (noticeable only for non English users)

* Fix spacing and consistency issues and debug warning due to improper flex
  grid sizer in module editor module properties dialog.
* Fix spacing and consistency issues in Pcbnew module properties dialog.
* Fix spelling error in DRC dialog message box text.

Eeschema: fix broken  mirroring for texts and labels in block mirror X and Y (this fixes Bug #1135505)
Pcbnew: add in module popup menu an option to edit the footprint in Modedit (like in Eeschema for components)
minor icons enhancements.

CMakeLists.txt: use elseif token instead of elif which create strange issues with some cmake versions.
Fix minor issues in nsis config files

Fix minor issues in nsis config files

* Make Pcbnew net list dialog honor escape key on Linux.
* Make Pcbnew swap layers dialog honor escape key on Linux.
* Layout and UI policy fixes for Pcbnew swap layer and net list dialogs.
* Layout and UI policy fixes for Eeschema plot dialog.
* Rename fpip.h to fpid.h.
* Fix FPID class compiler errors.
* Restore fpid.cpp to Pcbnew static library source list.

wxID_CANCEL, 5 pixel border around sizers, resizable search combobox, dialog_shim usage on a few dialogs

Pcbnew: plot Dialog: add a popup menu (try mouse right click in plot dialog) to selected/unselect groups of layers to plot.
All: For new zoom centering option: use Shift+Ctrl key instead of Alt key to select the new zoom centering, because Alt key has a special function under Windows.
2 very minor other changes.