xserver: Changes to 'dri2-swapbuffers'

[Jesse Barnes]

New branch 'dri2-swapbuffers' available with the following commits:
commit 84f380892456ce79bc0808aa54c57238217e1807
Author: Jesse Barnes <jbarnes at virtuousgeek.org>
Date:   Fri May 1 14:39:17 2009 -0700

    DRI2: add support for SwapBuffers request
    
    Support the new SwapBuffers DRI2 protocol request.  Requires that low
    level drivers have a SwapBuffers callback themselves.