Incorrect warnings about unqualified imports being redundant

Mixing qualified and unqualified imports can confuse the compiler.

To reproduce:

Create the file BadWarning.hs.

module BadWarning where

import Data.Map
import qualified Data.Map as M

example = empty

Run ghci -W BadWarning.hs, and you get:

BadWarning.hs:4:1:
    Warning: The import of `Data.Map' is redundant
               except perhaps to import instances from `Data.Map'
             To import instances alone, use: import Data.Map()
Ok, modules loaded: BadWarning.

This looks similar to #3992 (closed), but that bug does not repro for me, so I think the issue is slightly different.

Trac metadata

Trac field	Value
Version	7.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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