Merge branch 'jc/show-usage-help'

The help text from "git $cmd -h" appear on the standard output for
some $cmd and the standard error for others.  The built-in commands
have been fixed to show them on the standard output consistently.

* jc/show-usage-help:
  builtin: send usage() help text to standard output
  oddballs: send usage() help text to standard output
  builtins: send usage_with_options() help text to standard output
  usage: add show_usage_if_asked()
  parse-options: add show_usage_with_options_if_asked()
  t0012: optionally check that "-h" output goes to stdout

builtin/index-pack.c

@@ -1900,8 +1900,7 @@ int cmd_index_pack(int argc,
 	 */
 	fetch_if_missing = 0;
 
-	if (argc == 2 && !strcmp(argv[1], "-h"))
-		usage(index_pack_usage);
+	show_usage_if_asked(argc, argv, index_pack_usage);
 
 	disable_replace_refs();
 	fsck_options.walk = mark_link;