resolutions are 512x384, 640x480, 800x600, 1024x768 and 1280x1024 (the prefs
editor has to be updated to reflect this). The resolution selected in the
prefs editor is used as the default, but it can be changed in the Monitors
control panel. So far only tested with direct addressing.
contains all supported depths, default mode is stored in XPRAM upon startup,
and added video_switch_to_mode() call (currently unimplemented in all drivers)