Code in GPU_buffers_free was already trying to be safe
for threading, by skipping OGL calls there, but in fact
it was still buggy.
Namely, freeing was doing buffers shift in a cycle, and
if two threads will call this function shifting will go
crazy.
Now made it so GPU_buffers_alloc and GPU_buffers_free
are using mutex lock, so they're completely safe for
threading. Same goes to gpu_buffer_setup function.
It required minor functions reshuffle, so there're no
locks happening from locked thread, but it's all very
straightforward change
--
svn merge -r58276:58277 ^/branches/soc-2013-depsgraph_mt
b9ae749480