Change the default for the pridialplan parameter to the far more common case of

'unknown', and better document the use of each parameter.
(closes issue #12633)
 Reported by: tzafrir
 Patches: 
       pridialplan_unknown_2.diff uploaded by tzafrir (license 46)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@117182 65c4cc65-6c06-0410-ace0-fbb531ad65f3