xfce-nm-image: fix gdm install

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
angstrom-mesa-tweaks: disable GLES1 for mesa-demos

This is needed for e.g. raspberrypi to build xbmc

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>