`cabal check` should recommend against using the `stability` field

It seems to be consensus that the `stability` field is often misleading and shouldn't be used any more. See for example [Simon Marlow's comment on this issue](http://stackoverflow.com/a/3847493/1013393).

Therefore I propose that `cabal check` should discourage any explicit settings in the `stability` field.

As the `stability` field can also be set on a per-module basis (see e.g. [Data.Set](http://hackage.haskell.org/package/containers-0.5.9.1/docs/Data-Set.html)), I'd like `cabal check` to check all the modules too. My questions are:

1. Is checking the modules within the scope of `cabal check`?
2. Is the machinery for checking modules already in place?