Add a new flag 'd' (with optional context) permitting any extension within

that context to be entered as a new extension during the playback of a
voicemail greeting.
Patch inspired by bluecrow76, by tilghman.
(Closes issue #7063)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@97305 65c4cc65-6c06-0410-ace0-fbb531ad65f3