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

revision.h

@@ -82,6 +82,11 @@ struct rev_info {
 	 */
 	int rev_input_given;
 
+	/*
+	 * Whether we read from stdin due to the --stdin option.
+	 */
+	int read_from_stdin;
+
 	/* topo-sort */
 	enum rev_sort_order sort_order;