Use more reasonable cause code when rejecting incoming call waiting calls.

Use more reasonable cause code when rejecting incoming call waiting calls.

(closes issue ASTERISK-19397)
Reported by: Birger Harzenetter
Patches:
      nochannel-cause.patch (license #5870) patch uploaded by Birger Harzenetter
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Merged revisions 357407 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 357408 from http://svn.asterisk.org/svn/asterisk/branches/10

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@357409 65c4cc65-6c06-0410-ace0-fbb531ad65f3