CuDNN R2 fixes

CuDNN guys released a new version of their library, this PR fixes everything for the API changes.

Notably, the pooling operations also now have free zero padding if you wish so.
They introduced VolumetricConvolutions with this release, but i did not write a binding for that yet, but I changed the SpatialConvolution and Pooling to use their "N-dimensional" API.