Start copying files from xf86-video-nested project.
Get rid of nested-input-driver stuff for now.

We can readd it later, but it's not a priority for multiseat.
Start copying Xephyr files.
Set DISPLAY environment variable when Option "Display" is set in xorg.conf.
Add new xorg.conf option "Xauthority" for host X server auth file.
Fix coding style.