for-each-ref: add '--contains' option

Add the '--contains' option provided by 'ref-filter'. The '--contains'
option lists only refs which contain the mentioned commit (HEAD if no
commit is explicitly given).

Add documentation and tests for the same.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/for-each-ref.c b/builtin/for-each-ref.c
index 7521850..40f343b 100644
--- a/builtin/for-each-ref.c
+++ b/builtin/for-each-ref.c
@@ -9,6 +9,7 @@
 	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>]]"),
 	NULL
 };
 
@@ -41,6 +42,7 @@
 			     parse_opt_object_name),
 		OPT_MERGED(&filter, N_("print only refs that are merged")),
 		OPT_NO_MERGED(&filter, N_("print only refs that are not merged")),
+		OPT_CONTAINS(&filter.with_commit, N_("print only refs which contain the commit")),
 		OPT_END(),
 	};