Add two new dialplan variables when using features

Added DYNAMIC_FEATURENAME which holds the last triggered dynamic feature.
Added DYNAMIC_PEERNAME which holds the unique channel name on the other side
and is set when a dynamic feature is triggered.

(closes issue #14663)
Reported by: tamiel
Patches:
      20090313_features.diff uploaded by tamiel (license 712)
Tested by: tamiel


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@214309 65c4cc65-6c06-0410-ace0-fbb531ad65f3