Fixes for issues observed on MMVA: Clean up child processes on intentional termination of gardener, clean up npm's temporary directory after installation, cosmetic fixes

Hey Ryan,

Would you mind taking a quick look at this? We'd like to merge these in and do another release of gardener in a few days from now if that's okay. @garethbowen is working on one more patch for an issue where termination of a gardener module could cause gardener to stop trying to restart it; after that and a quick review/okay from you we should be ready.

If it's okay with you, we'd like to call this Gardener 1.04 and pack it with the next release of MMVA.

(N.B. FWIW, we're using `process.stderr.write` instead of `logger.info` due to the synchronicity requirements inside of signal handlers. Also, I take it Node somehow defeats the usual parent-termination-kills-children behavior via `setsid()` or similar? We looked all over the place for a `.unref()` or some kind of disown-ish call but couldn't find anything.)

Hope all is well!

Dave