A named outer is suitable when dealing with IntegrityErrors. It only
checks that it is not nested under an atomic only if it is nested
under enable_outer_atomic(name=<name>). This way only the view which
is causing IntegrityErrors needs to have its automatic transaction
management disabled and other callers are not effected.

By default, migrations are applied as they always have been. Exporting DISABLE_MIGRATIONS=1 or passing --disable-migrations to Paver commands will create tables directly from apps' models.

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

1 level of transactions.

TNL-367

This decorator executes the decorated function inside a
transaction with isolation level set to READ COMMITTED.

TNL-367