Break out pull --rebase into fetch; rebase --autostash

...this should make auto-updating a little less of a perpetual fail for those
of us with a tendency to tinker.

Not that anyone who uses zsh and oh-my-zsh would have such a tendency :)
Merge branch 'topic/update-autostash'

* topic/update-autostash:
  Break out pull --rebase into fetch; rebase --autostash