Add fix for longstanding bug in contribution_tracking DB

See http://www.mediawiki.org/wiki/User:MarkTraceur/FR-tech_setup_notes
for the messed-up manual query I had to run while installing CT for the
first time. I don't want that to be part of the setup. So let's fix this
in a normal...ish way.

Change-Id: Ie85278fb22a8b857ba086a69383c48f0789f9542
Merge "Add fix for longstanding bug in contribution_tracking DB"