padding support for dnn_conv
better interface for dnn_conv
test case for dnn_conv with padding
test other border_mode
Maybe I did something wrong, or the padding in GpuCorrMM is wrong
well, it is cross correlation, not conv
Merge pull request #2259 from jia-kai/master

padding support for dnn_conv
Merge pull request #2272 from f0k/conv-direction-hints

Make automatic insertions of dnn_conv() use the optimal cuDNN code path
Annotate ConvOp and GpuConv with direction hint and use this to select algorithm in conv_dnn optimizer