Annotate ConvOp and GpuConv with direction hint and use this to select algorithm in conv_dnn optimizer
Removed superfluous gpu_contiguous() in local_conv_dnn optimizer
Allow alternative cuDNN ops in convolution tests
Handle direction_hint when unpickling old ops
Merge pull request #2273 from f0k/conv-direction-hints

Make automatic insertions of dnn_conv() use the optimal cuDNN code path (2)