This function doesn't require the whole UserProfile object to
create the avatar url, and we call it from Message.to_dict_uncached().
(imported from commit e814caab101c4fedd1ba66df041a3408014e4085)
This needs to be deployed to both staging and prod at the same
off-peak time (and the schema migration run).
At the time it is deployed, we need to make a few changes directly in
the database:
(1) UPDATE django_content_type set app_label='zerver' where app_label='zephyr';
(2) UPDATE south_migrationhistory set app_name='zerver' where app_name='zephyr';
(imported from commit eb3fd719571740189514ef0b884738cb30df1320)
Kevin Mehall
Steve Howell
Tim Abbott