Use sharing in the Alternative instance of Maybe

The <|> method of the Alternative instance of Maybe does not share its first argument when it could:

instance Alternative Maybe where
    empty = Nothing
    Nothing <|> p = p
    Just x  <|> _ = Just x

I propose to share this argument:

instance Alternative Maybe where
    empty = Nothing
    Nothing <|> r = r
    l       <|> _ = l

Trac metadata

Trac field	Value
Version	7.2.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
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