Merge branch 'ab/do-not-limit-stash-help-to-push'

"git stash" by default triggers its "push" action, but its
implementation also made "git stash -h" to show short help only for
"git stash push", which has been corrected.

* ab/do-not-limit-stash-help-to-push:
  stash: don't show "git stash push" usage on bad "git stash" usage

diff --cc builtin/stash.c
Simple merge

diff --cc t/t3903-stash.sh
Simple merge