run-tests: exit cleanly if parallel run is interrupted
If interrupted while running with "--jobs N", run-tests asynchronously
spewed a bunch of output and backtraces from both the master and
slave processes, leaving the terminal full of goop. This patch makes
it behave more sensibly.
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.