Add dev/ folder to cmake

The [installation documentation](http://www.torch.ch/manual/install/index#devpackages) specifies that

>  Packages in dev are all compiled in the same way that the ones in packages sub-directory. We prefer to have this directory to make a clear difference between official packages and development packages.

However, it seems that `dev` is ignored by torch's make. The current patch fixes this. Or is `dev` now deprecated?