Given typeahed and the fact that this only worked if the person had a
full name that didn't contain whitespace, this side effect of the
original @shortname mentionfeature that we removed was experienced by
users as a bug.
Fixes#6142.
We want to avoid opening a DB connection in the markdown thread
as its DB connection might live for a long time
(imported from commit 7700b2ca793ee5e9add7f071b92f22a4bf576b3d)
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)