name shadowing warnings don't trigger on standalone declarations in ghci

The name shadowing warnings in ghci catch shadowing from top-level binds and let statements, but not from standalone declarations (new in 8.0).

rwbarton@morphism:/tmp$ ~/ghc-HEAD/bin/ghci -fwarn-name-shadowing
GHCi, version 8.1.20160212: http://www.haskell.org/ghc/  :? for help
Prelude> a <- return ()
Prelude> a <- return ()

<interactive>:2:1: warning:
    This binding for ‘a’ shadows the existing binding
      defined at <interactive>:1:1
Prelude> let b = return ()
Prelude> let b = return ()

<interactive>:4:5: warning:
    This binding for ‘b’ shadows the existing binding
      defined at <interactive>:3:5
Prelude> c = return ()
Prelude> c = return ()
Prelude>

I'm hoping this can be fixed for 8.0, since I would also very much like to turn on name shadowing warnings in ghci by default (in the interactive flags), to reduce confusion from examples like the below, which is now possible for the first time in 8.0:

Prelude> fact 0 = 1
Prelude> fact n = n * fact (n-1)
Prelude> fact 5
^C^CInterrupted.
Prelude> -- why did it run forever?

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	GHCi
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