WIP: depth-stencil hacks
I don't think all of these really makes sense, I just wanted to get some visibility to these patches that I've looked at while trying to fix problems with depth-stencil blits(?) in the GL3.3 CTS on Intel and NVIDIA HW.
These don't end up fixing the problem, but I think it does show that we don't always do the right things in this area. Suggestions on how to do these things better is very welcome.