Merge branch 'aw/numbered-stash'

The user always has to say "stash@{$N}" when naming a single element in the default location of the stash, i.e. reflogs in refs/stash. The "git stash" command learned to accept "git stash apply 4" as a short-hand for "git stash apply stash@{4}". * aw/numbered-stash: stash: allow stashes to be referenced by index only