Outgoing calls with Google Voice

Google has recently make some changes (again) to their protocol.  Rather then
patching asterisk to flip between the two different methods, we now allow both.

Lets hope this keeps Google Voice happy for a while.

(closes issue ASTERISK-18714)
Reported by: Iordan Iordanov
Patches:
    chan_gtalk.patch uploaded by Iordan Iordanov (licenses 6311)
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Merged revisions 341435 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 341436 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@341437 65c4cc65-6c06-0410-ace0-fbb531ad65f3