Bug 870171 - Part 19: Add attemptVacuum.
Bug 870171 - Part 20: Have BroadcastService start PruneService alarm.
Bug 870171 - Followup: Put deletion inside transactions, add final keyword.
Bug 870171 - Part 21: Take onCreate/onUpgrade out of a transaction.

While not strictly necessary since transactions can be nested, these
methods are contained in a transaction by default so pulling them out
should increase performance.