- Implement the assertion that the lock is already held, if we run
   ata_status_poll.

 - The usual host chip code load from Bartomiej onierkiewicz.  Fortunately
   I'm able to check the sis5513 fixes on a life system.

   More serious stuff... for IDE 88:

	- implement ata_best_pio_mode() in ata-timing.c
	  (play safer than driver's config_chipset_for_pio())

	- replace config_chipset_for_pio() by ata_best_pio_mode()
	  in host chips drivers
	  (trivial for hpt34x.c, hpt366.c and serverworks.c,
	   non-trivial for cmd64x.c and sis5513.c)

	- set PIO also for (U)DMA modes in cmd64x_tune_chipset()
	  (cmd64x.c)

	- fix bug in setting PIO0-2 for devices also supporting PIO3/4
	  (sis5513.c)

	- misc cleanups

 - Rename XXX_do_request back do do_request. This was just tmporary tagging.

 - Move ata_taskfile() call down to the ide-disk request handler.c, which is the
   only place needing it. Rename ata_taskfile to ata_do_taskfile().  This
   allowed us to implement the assertion that ata_do_taskfile() will be only
   called with the channel lock already held.