Fix delete cache so it also deletes location with run = None.
Merge pull request #3668 from edx/opaque-keys-fix-cache-content-diff-runs

Fix delete cache so it also deletes location with run = None.
Fix discussions by correctly serializing outgoing course_ids
Fixing ORA
Merge pull request #3674 from edx/flowerhack/fix-ora

Flowerhack/fix ora
fixup! Fix discussions by correctly serializing outgoing course_ids
Merge pull request #3669 from cpennington/opaque-keys-fix-discussion-tests

Fix discussions by correctly serializing outgoing course_ids
Migration refactoring
Let sql tell us if the data is unique
fixup! Migration refactoring