REFER_EVENT is missing from the message names array

REFER_EVENT has been added to switch_core_session_message_types_t
a while ago, but was never added to the message_names[] related array.

src/switch_core_session.c

@@ -752,6 +752,7 @@ static const char *message_names[] = {
 	"STUN_ERROR",
 	"MEDIA_RENEG",
 	"KEEPALIVE",
+	"REFER_EVENT",
 	"ANSWER_EVENT",
 	"PROGRESS_EVENT",
 	"RING_EVENT",