lots of fixes

- Fix the charmbits/service package so that it works, restarts the
service when the charm is upgraded and saves the output to a log file.

- Change gocharm so that it preserves the revision number in the charm,
working around a juju-core bug.

- Make the hook package validate hook names when registered.

- Make the example charm change its own persistent state only when it
has communicated that state where it needs to.