Provide a way to kill test runner thread

[neapel]

Occasionally the function under test has a bug that causes an infinite loop, for example:

(fact (repeatedly gensym) => nil)

The only way I've found to stop such a doomed infinite run is to kill the java process or exit the repl using ^D

Starting (autotest) from the REPL allows using it during the run, but issuing (autotest :stop) while a test is running (possibly infinitely) doesn't kill the running tests.

[marick]

Make (autotest :stop) kill the thread.