Fix build
Factorize gl headers include in a separate file.

It should avoid conflict with Xorg headers
Fix travis ci
Remove wrappers.
Add a "createVector" function for OSX
Use createVector in some others places
Add some ifdef for OSX
Add createVector in another place.
osx fixes
Merge branch 'texture-factorization' of https://github.com/supertuxkart/stk-code into texture-factorization

Conflicts:
	src/graphics/post_processing.cpp
Put some others bunch of code between ifdef win32
Add "functionnal" include in debug.cpp
Use VERSION_3_3 macro
Add some #if !defined(APPLE) in debug screen
Another ifdef sets...
Use createVector in others places
Replace std::vector<GLuint>{...} in post_processing
Another place found
Merge branch 'texture-factorization'
Fix OpenGL extension detection on Linux/Mesa.

Created function in glwrap to test whether a GL extension is available.
This required using OpenGL3's glGetStringi. Backwards compat code can
be added to function if necessary.