Relax revision check to allow modifying automatic flags
Relax revision check to allow modifying automatic flags

From the source code comment:

```hs
-- Automatic flags' defaults may be changed as they don't make new
-- configurations reachable by the solver that weren't before
--
-- Moreover, automatic flags may be converted into manual flags
-- but not the other way round.
--
-- NB: We always allow to change the flag description as it has
--     purely informational value
```

edsko/hackage-server,edsko/hackage-server