When should we allow self-qualification in lookupLocalRdrEnv

Currently, lookupLocalRdrEnv does not allow any qualification, not even when the qualification is the current module.

I believe this means that the following is accepted:

module M () where

x = 3
y = M.x

but the following is rejected:

module M () where
y = M.x
  where x = 3

This seems sort of reasonable, but I'm not sure if this behaviour is fully specified somewhere. If it is (e.g. in the Haskell report), then we should add a comment to lookupLocalRdrEnv to say so.