kwayland hardcodes to wayland-0 for the server ID, tweak it a bit so it uses WAYLAND_DISPLAY, as wayland-0 is in use on this system right from the first session

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@3046 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9