Updated upstream OpenGL header for 4.4.
Extended extension support bitset to handle MOAR of them.

160 should be enough for everyone ;-)
Support for ARB_texture_mirror_clamp_to_edge.

This functionality was present in ATI_texture_mirror_once and
EXT_texture_mirror_clamp for ages, now (strict subset of) it is in core
OpenGL 4.4 too.