GpuContiguous, tests, skip some cuda specific tests in opencl.

I think it should be in the graph, as if many node use the save variable and more then 1 need them as c contiguous, we would copy it many times. But I think we need to change how we do this. But this is for later. I think we need each op to declare the inputs strides accepted and outputs strides generated. That way, Theano can insert the conversion only when needed. This would be significant work and I let this to later. I just continue porting old Ops.