GLX_EXT_swap_control
http://www.opengl.org/registry/specs/gl/EXT/swap_control.txt
GLX_EXT_swap_control
	GLX_SWAP_INTERVAL_EXT 0x20F1
	GLX_MAX_SWAP_INTERVAL_EXT 0x20F2
	void glXSwapIntervalEXT (Display* dpy, GLXDrawable drawable, int interval)