Improve error reporting for message extraction failures
Improve error reporting for message extraction failures

* Emit a more reasonably-tagged metric for unexpected / semi-expected
  errors
* Expand the "ParseSSF-*" messages to say what they mean.

gphat/veneur,evanj/veneur,evanj/veneur,stripe/veneur,stripe/veneur,gphat/veneur,gphat/veneur,evanj/veneur