Fix Warning in AdvancedSubtensor.infer_shape.

This just remove warning and to not implement the case where the
warning was generated.
Fix test in debugmode
Fix cudnn tests
fix tests related to verify_grad
Fix tests. Add back old opt tag and test the new opt tag and the old one.
Fix test on python 3.
Disable cudnn pooling as we have problems with borders.
Merge pull request #2265 from nouiz/warning

Remove warning caused by AdvancedSubtensor.infer_shape.