Merge branch 'tg/stash-push'

"git stash save" takes a pathspec so that the local changes can be
stashed away only partially.

* tg/stash-push:
  stash: allow pathspecs in the no verb form
  stash: use stash_push for no verb form
  stash: teach 'push' (and 'create_stash') to honor pathspec
  stash: refactor stash_create
  stash: add test for the create command line arguments
  stash: introduce push verb