(MESS) astrocade: converted the expansion bus to be a slot
device, and converted RAM expansions to be slot cards. As a
result you now specify the expansion you want by using e.g.
    mess astrocde -exp blue_ram_32k
or the Slot Devices menu of the internal UI, instead of using the
DipSwitches menu. Check the -lslot output for a list of available
expansions. [Fabio Priuli]