Fix blits mostly on GLES but also on GL

This series fixes a number of piglits from

piglit run gpu -t blit -t gles

For GLES hosts the number of failures goes down from >100 to 33.. The piglit summary also reports a regression with MSAA depth blits, but this is not a true regression, because these blits to MS surfcaes via glBlitFramebuffer which is actually not supported on GLES and for some reason the piglit tests don't catch this. On the other hand resolving MS for depth textures via GL seems to be device dependent and would need additional information for the blit (i.e. zNear and zFar) so that MS-MS blits with depth textures are not possible to emulate accurately in a reasonable way, and hence will always fail on GLES. On a GL host this series also fixes #91 (closed).