Needs updating for PyTorch HEAD (no_grad)

[ezyang]

volatile is no more in PyTorch HEAD, which means that you have to use the no_grad context manager now. Any examples using volatile need to be ported accordingly. However, we shouldn't do this until the next release, because examples should work for the current release. (If someone wants to get the jump, maybe a dev branch is warranted.)

CC @colesbury

[ssnl]

Also we should update the doc on no_grad before next release.

[ssnl]

We probably should start a branch with updated scripts as people are starting to compile from source by themselves.