OSX has their own driver, so performance issues aren't shared with the nvidia driver (unlike the closed source linux and windows nvidia driver). So now they'll also use the MapAndSync backend like all other osx drivers.
fixes issue 6596
I've also cleaned up the if/else block selecting the best backend a bit.
The old way was to use big switch/case statements based on a type of buffer.
The new one is to use inheritance.
This change prohibits us to change the buffer type while running, but I doubt we'll ever do so.
Performance should also be a bit better. Also a nice cleanup.
Added some comments about this different kind of buffers.
This is a bit slower on map_and_* because of flushing and _very_ much slower on buffer(sub)?data because of a new memcpy.
But this design allow us to decode directly into a gpu buffer, eg vertexloader will profit :)
degasus