Minor IRCBot fixes/upgrades

Summary:
Keep him from getting killed every 24 hours by the overseer, add basic commit
support.

Test Plan:
Ran irc bot, fed him a commit, fed him "http://blah/D1".

Reviewed By: aran
Reviewers: aran, jungejason, tuomaspelkonen, codeblock, mroch
CC: aran, epriestley
Differential Revision: 377