Merge NAPTR support into trunk.

This adds NAPTR record allocation and sorting, as well as
unit tests that verify that NAPTR records are parsed and
sorted correctly.

Review: https://reviewboard.asterisk.org/r/4542



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@434068 65c4cc65-6c06-0410-ace0-fbb531ad65f3