configs/voicemail.conf.sample - Make mailcmd sample text more explicit

configs/voicemail.conf.sample - Make mailcmd sample text more explicit

Made the wording a bit more explicit. Didn't really change the meaning.
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Merged revisions 408876 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 408877 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 408878 from http://svn.asterisk.org/svn/asterisk/branches/12

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@408879 65c4cc65-6c06-0410-ace0-fbb531ad65f3