Features/issue 246

@cramaken @rafrombrc doh.  i had a bad length check here: https://github.com/mozilla-services/heka/commit/0fabcffc7589fa55fac8ca205095e06eb4f5604a#L0L418

This works on my laptop using real log files without reprocessing logfiles as I saw in https://github.com/mozilla-services/heka/pull/254#issuecomment-19413778