[Cairo] [patch] implement push/pull on xc surfaces

[Carl Worth]

On Sep 13, Eric Christopherson wrote:
 > (I still wasn't able to get the examples to run under vncserver or
 > Xnest.)

*grumble*

I said I had committed a fix for this, but I just found the code
sitting here uncommitted this morning. Now, it is committed. Please try
again.

-Carl