Clarify in extesions.conf.sample that there must always be a priority 1 for an...

Clarify in extesions.conf.sample that there must always be a priority 1 for an extension to be valid


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3496 65c4cc65-6c06-0410-ace0-fbb531ad65f3