Lightweight Java Game Library Code

Converted native code from C++ (.cpp files) to C (.c files), thus avoiding an annoying dependency on the standard C++ library on Linux. We weren't using any particular C++ features anyway.

Fixed WIN32->_WIN32 conditional in NVVertexArrayRange.cpp

Move native stub initialization from extgl into GLContext.java. Makes it much easier to
exlude extensions classes. Furthermore, GLContext.useContext(null) can now be used to
reset the native stubs when no context is current.

header unification

Various fixes

New extensions and static import modifications

Generalized function pointer initialization

Removed GL_CHECK_ERROR

Fixed win32 compile

Replaced CHECK_EXISTS with one time check at symbol load time