Improved mapping of extension states from combined device states.

Improved mapping of extension states from combined device states.

This fixes a few issues with incorrect extension states and adds
a cli command, core show device2extenstate, to display all possible
state mappings.

(closes issue #15413)
Reported by: legart
Patches:
      exten_helper.diff uploaded by dvossel (license 671)
Tested by: dvossel, legart, amilcar

Review: https://reviewboard.asterisk.org/r/301/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@204681 65c4cc65-6c06-0410-ace0-fbb531ad65f3