GLX_NV_swap_group
http://www.opengl.org/registry/specs/NV/glx_swap_group.txt
	Bool glXBindSwapBarrierNV (Display* dpy, GLuint group, GLuint barrier)
	Bool glXJoinSwapGroupNV (Display* dpy, GLXDrawable drawable, GLuint group)
	Bool glXQueryFrameCountNV (Display* dpy, int screen, GLuint *count)
	Bool glXQueryMaxSwapGroupsNV (Display* dpy, int screen, GLuint *maxGroups, GLuint *maxBarriers)
	Bool glXQuerySwapGroupNV (Display* dpy, GLXDrawable drawable, GLuint *group, GLuint *barrier)
	Bool glXResetFrameCountNV (Display* dpy, int screen)
