r9032 /src/mess/drivers/mz2500.c: [MZ-2500]: Many video related fixes, promoted system to working

http://mamedev.emulab.it/kale/?p=1210

And, for now I've made the Sharp X1 Turbo fix specific to the system, will see in future what's up with that (and the fact that it doesn't work with x1turbo40, that is very weird)