The following patch with some changes for trunk...

Merged revisions 126516 via svnmerge from 
https://origsvn.digium.com/svn/asterisk/branches/1.4

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r126516 | oej | 2008-06-30 14:50:55 +0200 (MÃ¥n, 30 Jun 2008) | 10 lines

Send all responses to an INVITE reliably, so that we retransmit if we don't get an ACK and
also fail if we don't get the very same precious ACK. Based on patch by tsearle, with
my own additions.

(closes issue #12951)

Reported by: tsearle
Patches: 
      busy_retransmit.patch uploaded by tsearle (license 373)

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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@126517 65c4cc65-6c06-0410-ace0-fbb531ad65f3