Try and improve the print-backtrace-and-exception/knots output, be
selective about the stack frames which are shown to try and produce
some useful output which reflects user code and hide the
&knots-exceptions.
This commit also introduces a bunch of tests scripts that produce
output from print-backtrace-and-exception/knots, to help test this
code in different situations.
I think this needs more work, maybe the thread pool should be more
similar to the resource pool, but I think the name change is still
helpful.
Maybe there's a need for a variable size thread pool and that can
better integrate with the work queue.
