Average pool CPU with python code

[CRASH] Make MaxAndArgmax support NoneConst as axis.

[TESTS] Fix crash in tests in debugmode and small optimizations.

Merge conv2

Added doc for strict flag.

Small doc fix gh-2793

Change cache refresh patter for speed up

Better error message when missing dimension in initial value in Scan

[TEST, BUILDBOT] Update tests since new optimization

Fix crash on Mac with curand op. We where using g++ extention that MSVC ...

[CRASH] Scan segfault with inconsistent inner graphs

[CRASH] Fix crash in save_mem when directly using outputs of the scan node

Define __ne__ as "not equal" by default in PureOp.

Remove the do_merge mechanism as it is dangerous and hard to use. Duplicate in inplace opt the node as needed.

Fix the merge of GpuDnnConv* by enabling again the merge of GpuAllocEmpty and fix the inplace by duplicating them in the inplace opt

finish gh-2768

[MRG] Faster test