Add assertion in nn.View constructor

Even though torch.view accepts a wildcard argument (-1) for one of the sizes,
nn.View cannot handle minibatches when using this option.
Add setNumInputDims() method to nn.View

This allows to use minibatches when using -1 for one of the sizes.
Merge pull request #24 from sergomezcol/master

Add mini-batch support for nn.View