Assign hack slowdown

[Robin Anil]

   if(f.apply(0, y) == 0) {
      it = iterateNonZero();
    } else {
      it = iterateAll();
    }

in assign function, this check is reducing the performance by a lot in many
of the algorithms where repeated assign is happening e.g LDA

What i propose i this. add 4 more types and make it is tested

SkipZeroBinaryFunction
SkipNoneBinaryFunction
SkipZeroUnaryFunction
SkipNoneUnaryFunction


Robin