naming convention should not fire off on reflected constraints; Alembic will also need adjustment

[Mike Bayer]

per #3817, alembic has a brittle reliance on naming conventions being applied at reflection time. We'd like to set up https://gerrit.sqlalchemy.org/#/c/209/ so that this isn't automatic but Alembic will also need to work around this.

[Mike Bayer]

alembic issue: https://bitbucket.org/zzzeek/alembic/issues/390/do-not-rely-on-reflection-applying-naming