Pcbnew: add WIN32_LEAN_AND_MEAN define in github_plugin.cpp. Note: this define is already in use in avhttp build (Windows specific)

* Add build type (debug/release) for wxWidgets library  versions greater
  than 2.8.
* Add build type (debug/release) for KiCad.
* Add missing build options.

* Modify error handling for OpenGL backend.
* Correct Doxygen comments notation.

build, it throws the time stamps away when there are edits to the CMakeLists.txt portion
pertaining to the external project.  Only a 'make clean' would remove the untarred tree.
This patch removes the need to do a make clean when changing the ExternalProject_Add()
text pertinent to patching.

Fixes bug 1250222 in KiCad-Winbuilder

GITHUB_PLUGIN uses redirected URL to remove one HTTP hit time.

* Pcbnew: catch exceptions when saving changes to footprint library table.
* Pcbnew: update footprint viewer library list if open when footprint library
  table changes.
* CvPcb: update library list when footprint library table changes.
* Minor coding policy fixes.

*) Move button handlers to LEFT MOUSE CLICK from COMMAND events, so wxGrid focus is not lost.
*) Sketch out the concept of COW support for the GITHUB_PLUGIN in its @todo.

https://svn.boost.org/trac/boost/ticket/8973
https://svn.boost.org/trac/boost/changeset/84950#file0

This is so builders with multiple out of source build trees can all use
the same common boost install directory.  And the build system will not
vascillate between the fuller and lesser subsets of boost.

All: under mingw32+msys: fix an issue when using Cmake version >= 2.8.5 which uses by default a response file.
This response file is not expanded under mingw3 2 (mingw/gcc bug?), and the list of include paths, found in this file, is not taken in account.
Now, under mingw32+msys, when not cross-compiling, the response file is disabled.
Cvpcb, Pcbnew: fix a list of libs  which should be added only when cross-compiling:
Previously, they were always added, which creates an issue with mingw/msy/ gcc  2.8.
Now they are added only when cross-compiling (this issue was noticeable only with msys+mingw version  2.8)

* Replace all occurrences of the word "part" with "unit" when referring to
  multiple unit components for improved consistency.
* Replace "shared by" with "common to" when referring to objects (lines, arcs,
  pins, etc.) that are common to all units.
* Improve wording in library component properties dialog.

* Build OpenSSL from source using the OpenSSL-CMake project on Windows with MinGW when no specifying OPENSSL_ROOT_DIR