Add detailed logging each time we checkForUpdates, to isolate race conditions.
Don't use both 'self' and 'this'. Fixes #11.

    I think the cause of #11 is that checkForUpdates is running inside a
    setInterval loop, where this._busy isn't getting set to the same thing
    as self._busy, causing parallel threads of execution.

    If we see more 'dueling deployers', this theory will be proven wrong :-P
Merge pull request #12 from 6a68/issue_11_dueling_deployers

Issue 11 dueling deployers