Add --jobs option to forall subcommand

Enable '--jobs' ('-j') option in the forall subcommand. For -jn
where n > 1, the '-p' option can no longer guarantee the
continuity of console output between the project header and the
output from the worker process.

SIG_INT is sent to all worker processes upon keyboard interrupt
(Ctrl+C).

Bug: Issue 105
Change-Id: If09afa2ed639d481ede64f28b641dc80d0b89a5c
1 file changed