for-each-ref: partly change <object> to <commit> in help

Change mentions of <object> to <commit> in the help output of
for-each-ref as appropriate.

Both --[no-]merged and --contains only take commits, but --points-at
can take any object, such as a tag pointing to a tree or blob.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/for-each-ref.c

@@ -8,8 +8,8 @@
 static char const * const for_each_ref_usage[] = {
 	N_("git for-each-ref [<options>] [<pattern>]"),
 	N_("git for-each-ref [--points-at <object>]"),
-	N_("git for-each-ref [(--merged | --no-merged) [<object>]]"),
-	N_("git for-each-ref [--contains [<object>]]"),
+	N_("git for-each-ref [(--merged | --no-merged) [<commit>]]"),
+	N_("git for-each-ref [--contains [<commit>]]"),
 	NULL
 };