Bugfix and reuse old code when the new one isn't used

This is needed when ndim !=2 and for older GPU like the GTX285.

It was always running inplace and it was alwayr considering the input as 2d.

Addressing code review comments obtained. Moving the code to c_support_apply_code  and handling the cases for launching the threads and blocks to be minimum of thresh-hold or what is required

REBASED: C code for GPUAdvancedIncSubtensor1.Handles one case to make it faster

add c_code_cache_version to GpuAdvancedIncSubtensor1 as it now have c_co...

No warning if g++ does not support -march=native

Instead of detecting llvm, we try to use -march=native, which is more
general.

Fix C code of GpuDownsampleFactorMaxGrad.

Use safe_new(x) instead of x.type() in scan grad.

Simpler graphs for canonical slices

This copies the test_value, making possible to use a test value
for sequences. Add test.

Moving an assert out of for loop (perf optimization) and adding back a declartion of a CudaNdarray_inplace_add

Compute hash on whole source file

Fix insertion of -arch=... when compiling with nvcc

Minor fixes

Fixes gh-1306

It used to be inserted only for the first Op after GPU initialization.

It was causing errors when running with cuda-memcheck, or when running
on Mac OS X.