OF-1788: Prevent race condition in unit test.
ArchiverTest suffered from a race condition that would occasionaly cause tests to fail. "Wait for complete" would occasionaly return, before the state of the DummyArchiver was completely up-to-date.
OF-1790: Database update scripts should handle empty table.
This modifies the update script to handle a scenario of an upgrade (as opposed to a fresh installation), but without having any logged MUC messages.
OF-1790: Initialize ofID sequences.
An earlier change introduced a new ofID-based sequence used for messageID, when writing MUC messages to the database. This commit initializes the counter that's used to the highest value that has already been logged.
