Generate response to Status Enquiry message with Status q.931 message.

Some PBXes require this for call status checking

(closes issue ASTERISK-18748)
Reported by: Fabrizio Lazzaretti
Patches:
      ASTERISK-18748-5.patch (License #5415) patch uploaded by may213
Tested by: Fabrizio Lazzaretti
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Merged revisions 344158 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 344159 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@344161 65c4cc65-6c06-0410-ace0-fbb531ad65f3