* Implement wglCreateContextAttribsARB hooks and other minor fixes:

  - Add wglCreateContextAttribsARB to WGL whitelist
  - Include wgl_enums.inc, wgl_ext_enums.inc in gl_types.h.
  - It seems that wglenum.spec and wglenumext.spec files have the WGL_ prefix baked where the GLX equivalents don't. Rather than fix the .spec files (which we don't own), fix the generator:
     - In voglgen.cpp, allow pPrefix to be NULL in gl_enums::dump_to_definition_macro_file.
     - If pPrefix is NULL, don't prepend anything to the enum name.
     - For wglenums.inc and wgl_ext_enums.inc, pass pPrefix as NULL.
  - In vogl_intercept.cpp, actual implementation of wglCreateContextAttribsARB based off GLX version.
  - Explicitly use WINAPI calling convention for WGL interceptors. WINAPI is __stdcall and the default for MSVC is __cdecl. This was triggering asserts due to stack corruption on some functions.