allocate-revision-karma.py is being very slow post the postgres 8.4 upgrade

[Steve McInerney]

when killed had been running for ~ 25 hours.
stub suggests that:

<stub> SELECT Revision.date_created, Revision.gpgkey, Revision.id, Revision.karma_allocated, Revision.log_body, Revision.revision_author, Revision.revision_date, Revision.revision_id FROM Revision, RevisionAuthor, ValidPersonCache WHERE Revision.revision_author = RevisionAuthor.id AND RevisionAuthor.person = ValidPersonCache.id AND NOT Revision.karma_allocated AND EXISTS (SELECT true FROM Branch, BranchRevision WHERE BranchRevisio
<stub> Slooooow query
<stub> We will need to rewrite it for 8.4 - subselects are always a pain, and unfortunately we seem to have used them to optimize for PG 8.3

do have a gcore on loganberry; but the above sounds more useful to start with.