nn.Linear is more non-blocking

This PR makes nn.Linear non-blocking (in most cases). Includes unit tests. It should be backwards compatible.

Changed the transpose such that it is done in place as suggested by @andresy 

fixes #33
fixes https://github.com/torch/nn/issues/77 (in most cases; when cublasSgemm permits)
depends on https://github.com/torch/nn/pull/89