Revert "st/dri: no need to request fake front buffer, only handle it being returned"

Revert "st/dri: no need to request fake front buffer, only handle it being returned"

This reverts commit 1336989ec60fff7bd590fefd28945a0e5dc536e3.

The commit breaks frontbuffer rendering and the possibility to do
on-demand frontbuffer requests on all Xservers prior to 1.7.

The commit should be conditioned on a dri2 version check.
I've submitted a patch to Xserver to bump dri2 minor, and it's acked by Ian.

To be able to check the version from within the state tracker, we will
probably need another dri2 extension function that returns the server
version. The protocol has support for it.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>