WL#4026: Foreign keys: mysql_upgrade for foreign keys

Affects: Server-6.1   —   Status: Un-Assigned   —   Priority: Low

When changing to the new foreign-key methods described in
WL#148 "Foreign keys: Implement Foreign Keys (all storage engines)"
users will encounter some incompatibilities if they have
foreign keys already.

The WL#148 LLD mentions this requirement.

There is an expectation that mysql_upgrade will change the .frm
as part of this task.