Split from #997. Maybe this should be specific to the win32 client (which may crash otherwise), maybe not.
It is actually quite hard to implement, and as it is things should not crash: we may fail to create an opengl window context but the code should fallback to a non-opengl window in that case.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1138