Not loading filesystem migrations when migrating down to a different app.

[seanharrison]

• When a "dn" migration in your app's filesystem migrations differs from the ones applied in the database,
• and the specified target "to" migration is in a different app (such as migrating down to the sqly init migration),
• then the app's filesystem migrations are not loaded,
• so the db-loaded migration is used.
• This can be vexing when bugfixing a dn migration, because the filesystem (corrected) migration is not loaded.

Workaround for now is not the migrate to a different app when bugfixing.