There are 256 filters in conv2.

AlexNet paper splits conv2 into two GPU's, each with 128 filters. Reference paper: http://www.cs.toronto.edu/~fritz/absps/imagenet.pdf Applying #528 to dev instead of master per @Yangqing.
Merge pull request #529 from crizCraig/patch-3

Fix example text: there are 256 filters in conv2.