XV cleanup series

[Eric Anholt]

Here's a pile of stuff I wrote when I was working on Xephyr XV with
glamor.  I wanted glamor to be able to create adaptors on its own
without needing cooperation from the DDX, and I didn't want to build a
third copy of DDX XV, so I was trying to clean up and share common
code.  I eventually backed off from that plan, but I've still got this
-500 lines of code left from when I was working on that.

This can be found on the "all-xv" branch of my tree.