removed GPC library due to its unacceptable license. Using the great and powerfull kbool library insteed

Fixed all related files also.

* MinGWResourceCompiler: change output directory and name of compiled resource file (old resource object files have to be deleted manually, eg. cvpcb/cvpcb_rc.o since the 'make clean' target does not remove them).
* Add some comments.

* Set a NAME_RESOURCES variable in MinGWResourceCompiler.
* Fix looking for zlib under msys (C:\msys\1.0). Minizip now builds under windows with external zlib.

* Add mingw_resource_compiler macro (Win32).
* Fix windres wxWidgets include paths (Win32).

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+eeschema
        * commiting my changes to allow multiple instances of a given schematic file within 
a hierarchy:
        ** internally, m_currentScreen has been replaced with m_currentSheet,
                which is a list or 'path' of screens.  The path of screens is used to 
generate
                a series of timestamps, which is converted to flat component reference via 
a look-up
                table in the schematic files.
        ** this means that m_currentScreen is no longer used -- use GetScreen().
        ** GetScreen is virtual, as some of the dialogs keep around a WinEDA_BaseScreen 
pointer.
        ** all sub-sheets in a given schematic must have different names to generate a 
meaningful netlist.

* Change tabs to spaces.
* Make Boost required.

This allows you to install only specific components (i.e. binaries, resources, doc files in specific languages), particularly useful for package mainatiners.
Default install will work as before (i.e. install everything).

* Add polygon library.