Implement WARPLossLayer

[kloudkl]

This PR sets the target of #126 to the dev branch and will continue to make it work with the other layers. For the detailed motivations, references and discussions, please refer to the original PR.

[zyan0]

@jay2002 👍 Thank you. You are right.
Is there anything helpful to print out in the forward function of WARPLossLayer?

[sergeyk]

@kloudkl The warp loss test currently fails for this PR. Do you intend to work further on this?

I have rebased your code on the latest dev, moving the WarpLossLayer definition to loss_layers.hpp, and making it a subclass of LossLayer. Please start with these changes: https://github.com/sergeyk/caffe/tree/kloudkl-warp_loss_layer

[kloudkl]

Thanks. I will complete it this month after finishing #415 and the Java API of Caffe in the spirit of OpenCV.

[bhack]

@shelhamer Core members can periodically review the status of old tickets like this one?

[elaksana]

@kloudkl Have you finished working on this? We have a new application in mind, and hopefully, it will be merged soon.

[shelhamer]

Closed as abandoned -- feel free to rescue if interested since a ranking loss could be useful.