OpenGL 3.2 support: make sure only available sampler types are used
OpenGL 3.2 support: VertexAttribLPointer is only available in OpenGL 4.2
OpenGL 3.2 support: added missing OpenGL 4.x requirements
Search for OpenGL library as well, it finds the right framework on the OS X
OpenGL 3.2 support: GL_PATCHES is only available in OpenGL 4.2
Find and include GLUT framework on OS X
Specify core profile 3.2 on OS X with GLUT to be able to use OpenGL 3.2 features