Ref T1191. Notable stuff:
- Adds --disable-utf8mb4 to bin/storage to make it easier to test what things will (approximately) do on old MySQL. This isn't 100% perfect but should catch all the major stuff. It basically makes us pretend the server is an old server.
- Require utf8mb4 to dump a quickstart.
- Fix some issues with quickstart generation, notably special casing the FULLTEXT handling.
- Add an --unsafe flag to bin/storage adjust to let it truncate data to fix schemata.
- Fix some old patches which don't work if the default table charset is utf8mb4.