more "free to wrong pool"

I've constructed a pretty reproducable program which gets
the "free to wrong pool" error using threads and LWP::Simple.

I've used semaphores to remove concurrency, and tracked
my particular problem into the vicinity of the ->request
method, where I am loth to try to follow it - needless
to say that's where all the complicated stuff happens.

In essence, my pared-down example does nothing except
fire up a bunch of threads, each of which does nothing
but LWP::getstore


-- posted in case anyone has any advice how to avoid
the problem (while still using threads), or in case
anyone needs an nice reliable example of a program
that crashes.