GLX_EXT_import_context
http://oss.sgi.com/projects/ogl-sample/registry/EXT/import_context.txt
	GLX_SHARE_CONTEXT_EXT 0x800A
	GLX_VISUAL_ID_EXT 0x800B
	GLX_SCREEN_EXT 0x800C
	void glXFreeContextEXT (Display* dpy, GLXContext context)
	GLXContextID glXGetContextIDEXT (const GLXContext context)
	GLXContext glXImportContextEXT (Display* dpy, GLXContextID contextID)
	int glXQueryContextInfoEXT (Display* dpy, GLXContext context, int attribute,int *value)
	typedef XID GLXContextID