improvements
1.  recognize any amd or intel part with the proper programming interface.

bug fixes
1.  properly recognize new media
2.  fix deadlocks when drives aren't responding.  (cf, d->active)
3.  properly deal with skipped ports.  for example, some chipsets
disable ports 0, 1 but enable port 2.  this resulted in unacknowleged
interrupts & hung machines.
4.  when a drive is removed, force d->sectors = 0.