Improve trace messages in debug/non-debug runs. In particular, shorted the
"waiting for resources" stuff.
Can kill comma-test-run with Ctrl-C when runs from the terminal prompt.
Keep the long-running xargs process on the background and communicate with
it using a FIFO. This way, the main process is in the wait state and can
handle signals immediately. Now can Ctrl-C from console and kill PID when on
the background, both the parallel and the serial versions.
Differentiate handling of SIGINT and other signals. Provide a wrapper
function for setting it up.