[PATCH] simple preemption debug check

[PATCH] simple preemption debug check

This simple check was first suggested by Andrew Morton.  Pretty basic -
whines if a task exits with a nonzero preempt_count value.

I put an identical check in the 2.4 preempt-kernel patch and - sure
enough - it was found that XFS essentially disables preemption as it
destroys data structures containing locks without first unlocking.  The
SGI folks are working on that.

Anyhow, its a quick and clean solution to debugging potential problems.
Patch is against 2.5.7, please apply.

	Robert Love