Calling other classes while garbage collection is generally dangerous and useless.

This happens with FXFileSelector.

FXWindow destructor calls recalc() and changeFocus() of it's parent windows.
Since these methods are routed back to Ruby code, but calling Ruby code from
GC isn't a good idea, we mark the parent window as "in_gc", so that it will
ignore recalc() and changeFocus() calls completely.

The parent window should also be scheduled to be free'd. In the other case,
the child window would have been marked as used.

fix retrieving of file handles, so that FXApp#addInput works with ruby 1.8.7, 1.9.2 and rubinius under Linux (win32 not tested yet)

support rubinius

C++ source and header files.