Better error message.
Don't reorder dimensions for elemwise when there is 0 or 1 dimensions.

this add extra useless code.
Add ScalarOp.c_code_contiguous interface and use it with exp.

Do this for amdlibm.

There is code for sigmoid, but it is disabled as it is slower.
Add contig version of pow, cos, sin, log, log2, log10
add amdlibm code for powx (pow(tensor, scalar))
fix test crash in debugmode.

it was triing the Image2Neibs.perform method for GpuImage2Neibs.
Fix Elemwise and CAReduce version when the scalar_op don't have a version.

We were not returning () when the scalar op don't have a version.
Merge pull request #1389 from nouiz/sigmoid

Sigmoid