Do a bit of code cleanup.

 - convert handling of IE PLTYPEs to switch statements
 - add braces to various small blocks
 - remove a bit of trailing whitespace
 - remove a couple of unnecessary ast_strdupa() uses


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@191848 65c4cc65-6c06-0410-ace0-fbb531ad65f3