- tests.
- Gearman::Server needs a fast "queue depth" command, along with
  Gearman::Client support so we don't have to manually do socket crap.
- Factor loop time for batch_run_sleep and only sleep the difference.
- Error handling needs to be sussed out everywhere.
- ::DB should use String::CRC32 to pick a dbid when uniqkeys are supplied.
  (same as Gearman::Client)
- Improve docs more? It's missing notes about DB scalability that it already
  does.
- Add some ASCII charts to describe flow better.
- Gearman::Server also needs batch job submission and batch job fetch
  commands. Mainly batch submission would speed things up a lot.