Blender Git Loki

get latest OpenGL version on Windows + AMD

When we ask for GL 3.2 compatibility profile:
AMD (Radeon HD 6970) gives us exactly this version
NVIDIA (Quadro K600) gives at least this version
Still need to check Intel behavior

We want *at least* the version requested, plus more recent features if
available.

Both GPUs tested & mentioned above are capable of GL 4.5. With this
commit they both give 4.5 to Blender.