Terminate child npm module processes when gardener is killed.

Prior to this patch, killing `gardener` with SIGTERM or SIGHUP caused `gardener`
to terminate in a way that left its children orphaned; these children were
automatically reparented to `init(1)` by the operating system, and a subsequent
restart of `gardener` would result in multiple running versions of a single
`gardener` module (process).

This patch handles `SIGTERM` and `SIGKILL` in the parent `gardener` process by
synchronously terminating all of the child processes in `running_processes` and,
in the case of SIGTERM, by then self-terminating. `SIGHUP` does everything but
self-terminate the parent process; `forever` automatically restarts everything
within a few seconds in a way that at least emulates a graceful restart.

Additional: Merge `tmp` cleanup patch from @garethbowen.
Cosmetic fixes.

Fix a couple typo/whitespace issues that were visible to users/administrators
via the CLI and log files.