Broker can be used with mappings not synchronized

If mapping synchronization fails once, then the next time creating a broker is attempted, it simply succeeds. This means running broker over problematic mappings, which is probably not cool.

JDBCBrokerFactory.newBrokerImpl(String, String) sets the "_synchronizedMappings" to true before calling the implementation, causing this. Setting the flag to true should be moved past the actual initialization call.