Adopt grml-live-remaster for live-boot's new /lib/live/mount/medium/
isolinux boot splashes: adjust path to grml-cheatcodes.txt
grml-cheatcodes: adjust live image path for new live-boot default
SW: add genisoimage to GRML_FULL

Required at least by grml-live-remaster (which is neither very
stable nor beautiful but anyway useful in certain situations, so
make its usage at least as easy as possible).

Thanks: Charles A. Hewson <cahewson@eskimo.com> for the bug report
Acked-by: Alexander Wirt <formorer@grml.org>