Merge branch 'tg/stash-with-pathspec-fix'

"git stash -- <pathspec>" incorrectly blew away untracked files in
the directory that matched the pathspec, which has been corrected.

* tg/stash-with-pathspec-fix:
  stash: don't delete untracked files that match pathspec

diff --cc git-stash.sh
Simple merge

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