Attempt to do something intelligent with IRQ handlers which don't return
IRQ_HANDLED.

- If they return neither IRQ_HANDLED nor IRQ_NONE, complain.

- If they return IRQ_NONE more than 99900 times in 100000 interrupts, complain
  and disable the IRQ.

  I did have it at 750-in-1000, but someone had an otherwise-functioning
  system which triggered it.

  The 99.9% ratio is designed to address the problem wherein the babbling
  device shares an IRQ with a good device.  We don't want the good device's
  trickle of IRQ_HANDLED callouts to defeat the lockup detector.  (fat chance
  os this working right).

- Add a kernel boot parameter `noirqdebug' to turn the whole thing off.