Fixed PairwiseDistance for odd Lp norms
Fixed the bprop in PairwiseDistance for pnorms other than one.  The gradInput has always been wrong it seems; the sign of the gradient is correct but the magnitude was wrong.  I also added a test in extra/nn/test/test.lua for nn.PairwiseDifference, which tests both the batch and non-batch code paths for a few different p-norms.
it seems like torch.abs() doesn't have a cuda implementation, so the previous commit would fail when PairwiseDistance():cuda() was called.
fixed a bug in Pairwise distance when the output Lp norm is zero (which results in a divide by zero issue).  Rewrote PairwiseDistance following Clement's suggestion to only have one codepath.  Fixed a small bug in extra/test/test.lua where the input to the non-batch fprop test was zero.
going back on Clement's suggestion.  It was a good idea, but we're needlessly loosing performance in the 1D case with the input clone.
Merge branch 'master' of github.com:torch/torch7-distro
Fixed a bug in PairwiseDistance where the gradInput table isn't converted when Module.type function is called (this bug has always existed and is not due to the recent changes).
Merge pull request #183 from jonathantompson/master

Fixed PairwiseDifference for norms other than 1