Implement segmented versions of scanl and scanr.
Implement segmented versions of scanl and scanr.

Ignore-this: deb76ac01e9735524b574f280e843e31

At the Prelude-level, implement segmented versions of scanl and scanr:
scanlSeg and scanrSeg, respectively. Use exisiting Accelerate AST
primitives only.

darcs-hash:20101109040010-c3ac2-0f70d61f5fa3739068bd9d92ea96d391803ead2a.gz

robeverest/accelerate,sjfloat/accelerate,robeverest/accelerate,wilbowma/accelerate,rrnewton/accelerate,wilbowma/accelerate