Created by: grygielski

Add LeakyReLU MKLDNN support v2. This version of code uses additional attribute added to activation grad operator op->SetAttr("forward_input_X", Input("X").back());. I tried different things but it looks like matching operator and its gradient is only possible through this unique string got from Input() function. Is this additional Attr also a problem for you? @luotao1 @sneaxiy