Comment 16 for bug 1238695

I abandoned my efforts in lp:~kdub/mir/snapshot-error-checking, as it turned out not to be that robust (errors were still being generated).

Rather, I kept investigating, and found that the same EGLImages bound in the rendering thread and the snapshot thread on this driver (but not any of the others) cause problems. I put a workaround for this (make different contexts generate EGLImage siblings) in lp:~kdub/mir/fix-1238695