Ok, I tracked the problem down. Basically what is happening is that
a new current user lwp is selected while other user threads are
sitting in the LWKT run queue which have not yet had a chance to add
themselves back to the userland queue.
The problem is that I can't just cycle the run queue by calling
lwkt_switch(), because new user threads may pop onto it at any time.
I hope to be able to fix it tonight but it will require some
significant work and may extend into tomorrow.
-Matt
