Merge branch 'jk/rev-list-stdin-noop-is-ok'

"git rev-list --stdin </dev/null" used to be an error; it now shows no output without an error. "git rev-list --stdin --default HEAD" still falls back to the given default when nothing is given on the standard input. * jk/rev-list-stdin-noop-is-ok: rev-list: make empty --stdin not an error