adds compliance for mesa versions <9.2

Intel's integrated graphics use Mesa for hardware acceleration. Because the currently used ```glFramebufferTexture``` method got only implemented recently[1], it's not yet available (current Ubuntu deb version is 8.0.4, most recent Mesa version is 9.2).

To me (Mesa/OpenGL noob speaking) ```glFramebufferTexture2D``` looks like doing the same as ```glFramebufferTexture``` and so I switched them to enable support for older Mesa versions. Another way to solve this might be to get the latest Intel drivers from their repository [2], but then again they are probably not as thoroughly tested as the ones available through Ubuntu's repos.

[1] http://comments.gmane.org/gmane.comp.video.mesa3d.devel/57128
[2] https://01.org/linuxgraphics/

PS: This fixes the segfault problem described in issue #315