Fixed #117 for SP. No longer checking Nvidia extension stuff on
non-supporting cards.
Removed unused class, probably for Xbox RTT (Render-to-Texture)
Merge pull request #211 from xycaleth/master

Fix for #117, and removed unused class.
Improved extension detection similar to 27ea81a4 and 4df61444.
Fixed a crash with previous commit.
Merge pull request #213 from xycaleth/master

Improved GL extension checking/detection.
Removed Q_stristr from code/sdl/sdl_glimp.cpp