HEAD freezes

[Matthew Dillon]

    Ok, I'm close to tracking this one down.  It's a critical section
    mismatch somewhere.  A critical section gets entered and never gets
    released, the user process then runs in a critical section which as
    you can imagine can lead to, oh, things like interrupts not working
    any more, and infinite loops locking up the box as well.

    I am adding INVARIANTS code to panic if the critical section count
    becomes mismatched and hopefully I'll track down the current mismatch
    soon.

						-Matt