We can safely ignore the presence of the extra tables that could be
left behind in the database from when we had these installed (before
Zulip 1.7.0 and 2.0.0, respectively).
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Attempting to "upgrade" from `main` to 4.x should abort; Django does
not prevent running old code against the new database (though it
likely errors at runtime), and `./manage.py migrate` from the old
version during the "upgrade" does not downgrade the database, since
the migrations are entirely missing in that directory, so don't get
reversed.
Compare the list of applied migrations to the list of on-disk
migrations, and abort if there are applied migrations which are not
found on disk.
Fixes: #19284.
Anders Kaseorg
Alex Vandiver
Tim Abbott