Assign message ids manually

Instead of using AUTO_INCREMENT. First step of issue #22.
Query subscriptions for a message separately

Part of issue #22.
Split up the prepare queue from the save queue

Getting there. But we still can't deliver the messages earlier until queues can
be queried. Issue #22.
JobQueue#jobs

Issue #22.
Dump the entire query when slow

Useful to see the parameters. Lets me EXPLAIN it.
Route all getMessages calls through Subscriber

Issue #22.
Move the limit stuff to subscriber

Issue #22.
Store user ids as a dictionary

Will be useful for the subscriber soon.
Punt inclusive parameter from getMessages

Instead, adjust for it before querying. Simplifies things for issue #22.
Make messages available immediate

Issue #22.
Typo
Serialize the queue on exit

So we don't lose them. Although I don't know if this code is really needed.
Meh. Issue #22.