UPGRADE: Note IAX2 compatibility issue between 1.4 and 1.8+ systems.
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Merged revisions 411457 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@411458 f38db490-d61c-443f-a65b-d21fe96a405b