Deleting a milestone should delete its attachments

[Peter Suter]

Deleting a milestone does not delete its attachments. (As previously discussed.)

Proposed fix:

trac/ticket/model.py

@@ -1011 +1011 @@
         with self.env.db_transaction as db:
             self.env.log.info("Deleting milestone %s", self.name)
             db("DELETE FROM milestone WHERE name=%s", (self.name,))
+            Attachment.delete_all(self.env, self.realm, self.name)
             # Don't translate ticket comment (comment:40:ticket:5658)
             self.move_tickets(retarget_to, author, "Milestone deleted")
             self._old['name'] = None

Reparenting of attachments when a milestone is renamed was previously fixed in #7933 and a unit test was added.

A similar unit test should be added for deleting attachments.

[Peter Suter]

In the attached patch I rebased the proposed fix for 0.12.6 and added a unit test.