Add ($!!) and force to deepseq

For the related discussion on libraries@, please see http://www.haskell.org/pipermail/libraries/2011-July/016540.html

The result of the discussion was that $!! should be added to deepseq:

($!!) :: (NFData a) => (a -> b) ->a -> b
f $!! x = x `deepseq` f x

infixr 0 $!!

Also, that force should be added but with suitable documentation to indicate possible ways in which it may behave other than as you'd expect:

force :: (NFData a) => a -> a
force x = x `deepseq` x

Trac metadata

Trac field	Value
Version	7.0.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries (other)
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