Always include unexpected messages in vroom error output

Changes vroom to notice unexpected messages even in non-strict message modes and include them in the failure output if there was also a "real" failure to help with troubleshooting.

Fixes #56.

The code structure makes the implementation suck a little. Really, these Failure objects should be changed to not be implemented as Exceptions the way they currently are. I'd like to refactor that ugliness away eventually, but it's too big of a project for me to get to it in the short term.