Problematic migration

Initial state, release as it currently runs. 2 cohorts have been enabled, and one user is in both of them simultaneously.

Database queries at that time
mysql> select * from course_groups_cohortmembership;
ERROR 1146 (42S02): Table 'edxapp.course_groups_cohortmembership' doesn't exist
mysql> select * from course_groups_courseusergroup_users;
+----+--------------------+---------+
| id | courseusergroup_id | user_id |
+----+--------------------+---------+
|  3 |                  1 |       1 |
|  4 |                  1 |       3 |
|  2 |                  2 |       3 |
|  1 |                  2 |       4 |
+----+--------------------+---------+
4 rows in set (0.00 sec)

Now, we want to apply Eric's awesome new uniqueness constraints, so we begin by applying migrations 0005 and 0006.
Here's the same queries after that:
mysql> select * from course_groups_courseusergroup_users;
+----+--------------------+---------+
| id | courseusergroup_id | user_id |
+----+--------------------+---------+
|  3 |                  1 |       1 |
|  4 |                  1 |       3 |
|  1 |                  2 |       4 |
+----+--------------------+---------+
3 rows in set (0.00 sec)

mysql> select * from course_groups_cohortmembership;
+----+----------------------+---------+---------------------------------+
| id | course_user_group_id | user_id | course_id                       |
+----+----------------------+---------+---------------------------------+
|  1 |                    1 |       1 | course-v1:edX+DemoX+Demo_Course |
|  2 |                    1 |       3 | course-v1:edX+DemoX+Demo_Course |
|  3 |                    2 |       4 | course-v1:edX+DemoX+Demo_Course |
+----+----------------------+---------+---------------------------------+
3 rows in set (0.00 sec)

Hooray! user_id 3 was fixed!
But not so fast - the code changes aren't yet live, so we aren't enforcing the use of the CohortMembership table at all.
Now, the instructor moves all 3 users to a new cohort. Database shows:
mysql> select * from course_groups_courseusergroup_users;
+----+--------------------+---------+
| id | courseusergroup_id | user_id |
+----+--------------------+---------+
|  7 |                  3 |       1 |
|  6 |                  3 |       3 |
|  5 |                  3 |       4 |
+----+--------------------+---------+
3 rows in set (0.00 sec)

mysql> select * from course_groups_cohortmembership;
+----+----------------------+---------+---------------------------------+
| id | course_user_group_id | user_id | course_id                       |
+----+----------------------+---------+---------------------------------+
|  1 |                    1 |       1 | course-v1:edX+DemoX+Demo_Course |
|  2 |                    1 |       3 | course-v1:edX+DemoX+Demo_Course |
|  3 |                    2 |       4 | course-v1:edX+DemoX+Demo_Course |
+----+----------------------+---------+---------------------------------+
3 rows in set (0.00 sec)

So now the tables don't agree, and there's no easy way to fix them.

Update 11-02: this is the point at which we'd run the new post_cohort_membership_fix command to fix the database.