rev-list: honor --quiet option

Nick Andrew noticed that rev-list lets --quiet option to be parsed by
underlying diff_options parser but did not pick up the result.  This
resulted in --quiet option to become effectively a no-op.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-rev-list.c

@@ -597,6 +597,7 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 	revs.commit_format = CMIT_FMT_UNSPECIFIED;
 	argc = setup_revisions(argc, argv, &revs, NULL);
 
+	quiet = DIFF_OPT_TST(&revs.diffopt, QUIET);
 	for (i = 1 ; i < argc; i++) {
 		const char *arg = argv[i];
 
@@ -628,10 +629,6 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 			read_revisions_from_stdin(&revs);
 			continue;
 		}
-		if (!strcmp(arg, "--quiet")) {
-			quiet = 1;
-			continue;
-		}
 		usage(rev_list_usage);
 
 	}