fixed incorrect checking of the existence of GLX_EXT_swap_control and friends
[demo_prior] / libs /
drwxr-xr-x   ..
-rw-r--r-- 553 Makefile
drwxr-xr-x - cgmath
drwxr-xr-x - drawtext
drwxr-xr-x - glew
drwxr-xr-x - imago2
drwxr-xr-x - treestore