Start using i18n for user message lookups.

Notable big changes is that I try to offer suggestions as to what might
be wrong. Additionally, for unrecoverable failures, emit a big message
about how this is probably a bug and offer irc/mailing list/etc
- Fix logger setup in the new pipeline
- log backtraces from the agent if debug (-vv)
- more friendly error messages
- style tweaks to stdin plugin
- copy parse_config into agent2
- improve pipeline shutdown under agent2