Redirected XV (proposed API change)

[Aaron Plattner]

Since we're changing the ABI/API for 7.1, I figured now is a good time to add
redirected XV support to the DDX.  The proposed patch is here:

  http://people.freedesktop.org/~aplattner/xv-redirection-1.patch

The change adds a DrawablePtr parameter to the XV driver hooks responsible for XV
rendering.  Since this is an API change, I want to get feedback from this list
before checking it in.  What do you guys think?

A simple proof-of-concept implementation for the nv driver is here:

   http://people.freedesktop.org/~aplattner/nv-xv-redirection-1.patch

It only works for windows with backing pixmaps in VRAM.

-- Aaron Plattner