use copy instead of os.link since the latter might fail for various reasons

testrunner.py rewrite: remove stat printing functionality; store more data in db; more reliable killing of subprocesses

queue: add copy() method to queue classes; constructor now accepts optional items argument to initialize a queue with iterable

save&undo libev's SICHLD handler when installed; install it when first child is created or when install_sigchld() is called