BwAuthority postgres scanner freezes with changes from #3679 TorCtl Event Parsing Rewrite

BwAuthority, postgres, and the changes in legacy/trac#3679 (moved) provide the perfect storm for more BwAuthority freezes.

Initially everything works fine, but 2 days later 2 of my scanners had halted. I restarted them and another froze in about a day.

This looks similar to the problem arma raises in legacy/trac#3834 (moved), where the scanner freezes without WARN, ERROR, so it may be db locking related:

INFO[Tue Sep 13 16:16:38 2011]:Waiting on consensus result: False
DEBUG[Tue Sep 13 16:16:38 2011]:Deleting ignored stream: 12028
INFO[Tue Sep 13 16:16:38 2011]:Newdesc timer is up. Assuming we have full consensus
INFO[Tue Sep 13 16:16:38 2011]:Consensus change... Updating rank history

This problem appears to have been introduced or exposed with these changes. The bwauth VM and my testing vm have not frozen with the old Event Parsing code.