Fix several problems caused by multiple line usage with i2004 phones.
Reported by: Daniel Bohling, MihaiMircea

(closes issue ASTERISK-21061)
(closes issue ASTERISK-21120)
........

Merged revisions 389661 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@389663 65c4cc65-6c06-0410-ace0-fbb531ad65f3