update the internal cli api following comments from kevin.

This change basically simplifies the interface of the
new-style handler removing almost all the tricks used in
the previous implementation to achieve backward compatibility
(which is still present and guaranteed.)



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@47652 65c4cc65-6c06-0410-ace0-fbb531ad65f3