[Cogl] [Resend][Request] Cherry-pick commit 93b7b4c85

[Emil Velikov]

[Resending with slight variations, from a subscribed email]

Hello list

Recently I have noticed that performance of my gnome-shell has
"degraded". It is related to the fact that recent mesa has exposed
multisample visuals [1]. Additionally using multisampled visuals may
lead to crash in gnome-shell

A quick look at the cogl git repo indicates that a fix is present but
only in the master branch.

Thus can we cherry-pick commit 93b7b4c85 (glx do not use multisample
visual config for front or pixmap), for the 1.14 and 1.12 branches

A few "Why should we", arguments I believe are benefis
* Branch 1.14 is used by the latest gnome 3.8
* Branch 1.12 is used by the gnome 3.6 - the most common gnome 3 out there
* Improves performance
* Easy cherry-pick
* No perceived side effects

Thanks
Emil

[1] Commit 35840ab18(st/dri: implement MSAA for GLX/DRI2 framebuffers)