Updated to latest versions of alembic, billiard, celery and kombu.

Disable CELERYD_FORCE_EXECV as per celery changelog warning.
Downgrade irc to 9.0 as 10.0 drop Python 2.6 support.
Give all celery queues a prefix to better distinguish them in Redis.

Retain queues with the old name for one release, to make sure we
process any remaining jobs in those queues.