VID_Init now takes mode settings (fullscreen, width, height)

VID_Init now takes mode settings (fullscreen, width, height)
commandline options like -window and -width are now parsed by vid_shared code
vid_width, vid_height, and vid_bitsperpixel cvars added, vid_mode removed
VID_CompareMode added, for simpler mode matching (returns a double, smaller value is better match)
GL_OpenLibrary takes a library name to load
GL_OpenLibrary, GL_CloseLibrary, and GL_GetProcAddress have been moved to platform specific vid_ files (wgl and glx)
gl_platform added (example values: "WGL", "GLX")
gl_platformextensions added (containing any extensions reported by platform specific strings)
gl_checkextension renamed to GL_CheckExtension for consistency
glXQueryExtensionsString and glXGetProcAddressARB support
looks up GLX_SGI_video_sync extension
removed halfscreen hack from vid_wgl (the code that tried to identify dual monitor configurations and use only one of them)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@2363 d7cf8633-e32d-0410-b094-e92efae38249