Storable instance for Complex

I propose that the following instance be added to base:

instance (RealFloat a, Storable a) => Storable (Complex a) where
    sizeOf z    = 2 * sizeOf (realPart z)
    alignment z = sizeOf (realPart z)
    peek p = do
        [r,i] <- peekArray 2 (castPtr p)
        return (r :+ i)
    poke p (r :+ i) = pokeArray (castPtr p) [r,i]

This instance is binary compatible with C99, C++ and Fortran complex types.

It is currently needed by at least two independent packages: hmatrix and fft. Since it is natural for user code to use both of these packages, we need to move the instance to a common location.

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions
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Blocking
CC
Operating system	Multiple
Architecture	Multiple