update comment for backpermute skeleton
update comment for backpermute skeleton

Ignore-this: fe6efe126167de85b2044bfacff09344

darcs-hash:20100715072349-dcabc-10de495e880facf92af774f2c9226e2a1347e487.gz

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