С утра пораньше меня вштырил ваш вопрос) Вот чего нашлаGenerally the phenomenon is called the intrusive consonant.Messenger shows us a case of "intrusive N" or "parasitic N." Nasal consonants are often used in this way, but not exclusively nasals.From http://www.etymonline.com/index.php?term=messengerWith parasitic -n- inserted by c. 1300 for no apparent reason except that people liked to say it that way (compare passenger, harbinger, scavenger).Please see the similar etymology for passage --> passenger.