Add description to manager_action structure, and add some comments.

Add ast_manager_register2 which adds description as an additional arg
Rework how events are added so they get ordered alphabetically
Add 'show manager command <commandname>' (with tab completion) to
	view info on each command

Added descriptions to 'Ping' and 'Originate' but they kinda suck, so we
need other people to come up with good descriptions for each of the
manager commands.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@3132 65c4cc65-6c06-0410-ace0-fbb531ad65f3