This fixes following issues for PIO-in:
 - shared PCI IRQs handling
 - fail request if the last status is bad
and PIO-out:
 - set hwgroup->handler/timer in prehandlers
 - handle drive->unmask in prehandlers
 - check for !rq->nr_sectors and DRQ_STAT bit set
 - use drive->bad_wstat instead of BAD_W_STAT
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@elka.pw.edu.pl>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>