Add ability to notify an external application/script that the voicemail password was,

while also still changing the password "internally".

Issue 7371, initial patch by pdunkel, with rewrite/config comments by me.
Additional modifications (yay bitmask) by pdunkel.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@47814 65c4cc65-6c06-0410-ace0-fbb531ad65f3