Added state aware guard to teapot_data.h
Justified my #include of freeglut_std.h in ext header
protected extern "C" by __cplusplus in input_devices.c + mswin
protected extern "C" by __cplusplus in fg_fgl2.h + .c
Added a guard to fg_structure to free callbacks if they are not state-aware
Added a guard to fg_structure to init statusFn to NULL if it's not state-aware
Patched internals so they can compile with STATE_AWARE switch (with a C compiler)
I decided to add FREEGLUT_STATE_AWARE_CALLBACKS as preprocessor def. This guard therefore is necessary
Updated CMakeLists to change language to C++ only when building with STATE_AWARE flag