Complex Convolutions

Here is the commit associated with:

https://github.com/torch/nn/pull/118

One thing that code reviewers should pay attention: TESTING.

Here's what I did.  I didn't write a CPU version (I just don't have time and I really don't need it), so instead I wrote a pure lua version of complex convolutions using SpatialConvolutionMM, table containers and additions / multiplies.  THEN, because this network needs testing, I did a complex correlation in Matlab for a very simple input case and made sure that the forward value matches the Matlab output.

The last part of this test is a little messy...  The input and output values are hard-coded, but I think this is the quickest and easiest way to ensure correctness (with a missing CPU implementation).