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

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