app_voicemail: Memory Leaks against tests

(issue ASTERISK-22467)
Reported by: Corey Farrell
Patches:
    app_voicemail-1.8.patch uploaded by coreyfarrell (license 5909)
    app_voicemail-11up.patch uploaded by coreyfarrell (license 5909)
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Merged revisions 401743 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 401744 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 401745 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@401746 65c4cc65-6c06-0410-ace0-fbb531ad65f3