megapc: correct CPU type to 386SX (no whatsnew)

git-svn-id: svn://dspnet.fr/mame/trunk@30227 749742ba-7341-0410-aadc-df50b521781e
pc_dsk: 1.2MB floppies have 80 tracks (nw)

git-svn-id: svn://dspnet.fr/mame/trunk@30228 749742ba-7341-0410-aadc-df50b521781e
Dirty modernization (nw)
ATTN:Aaron, please ignore this change, to prevent merge issues

git-svn-id: svn://dspnet.fr/mame/trunk@30229 749742ba-7341-0410-aadc-df50b521781e
Ah, and this one (nw)

git-svn-id: svn://dspnet.fr/mame/trunk@30230 749742ba-7341-0410-aadc-df50b521781e
Same for Amiga, so Duke ignore this one (nw)

git-svn-id: svn://dspnet.fr/mame/trunk@30231 749742ba-7341-0410-aadc-df50b521781e