Merge branch 'js/difftool-no-index'

"git difftool" can now run outside a repository.

* js/difftool-no-index:
  difftool: allow running outside Git worktrees with --no-index
  parse-options: make OPT_ARGUMENT() more useful
  difftool: remove obsolete (and misleading) comment

parse-options.c

@@ -288,6 +288,8 @@ again:
 					     optname(options, flags));
 			if (*rest)
 				continue;
+			if (options->value)
+				*(int *)options->value = options->defval;
 			p->out[p->cpidx++] = arg - 2;
 			return PARSE_OPT_DONE;
 		}