Port the bart stuff (log processing) to python.

Mostly so that we can do proper logging, send stats
to graphite, and manage with supervisord.
Factor signal registry into a util function.
Add better error handling and logging to bart.

Add --logfile option for easier manual testing.
Add in-memory rate limiting to bart.
Add error handling to log line processing.
Factor the statsd connection into smithers.
Switch to use the NFS to share latest log file name.
Merge pull request #86 from pmclanahan/bart-py

Port the bart stuff (log processing) to python.