Update CHANGES file for Asterisk 12

This updates the Asterisk 12 CHANGES file with the things that were missed
during the development cycle.

Review: https://reviewboard.asterisk.org/r/2795/
........

Merged revisions 397870 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@397872 65c4cc65-6c06-0410-ace0-fbb531ad65f3