When we insert a record in PostgreSQL and we specify the ID, the
internal ID sequence for that table isn't updated.
In order to keep the original IDs so we didn't break any foreign keys,
we specified the IDs when copying the table, resulting in a table having
its ID sequence with a value of an existing record. When trying to
insert a new record, we got a `PG::UniqueViolation` exception.
Updating the sequence after the data migration might not be the most
elegant solution, but it's easy to do and it's already been tested on a
production environment.
Calling `load_tasks` in several files made rails load the tasks several
times, and so they were executed several times when called.
Since the milestone migration can't be executed twice in a row (it would
fail with duplicated ID records), loading the tasks several times made
the milestone migrations task specs fail.
