fix remaining issues related to CUDA_KERNEL_LOOP
fix remaining lint errors
use CUDA_KERNEL_LOOP in padding layer
Merge pull request #240 from jeffdonahue/rm-cuda-kernel-loop-comments

Fix minor issues related to CUDA_KERNEL_LOOP -- merging myself as I'm only adding/removing comments other than the addition of CUDA_KERNEL_LOOP to PaddingLayer (and checked that this passes all tests).