Dns lua

This patchset adds 'dns.rrname' field to the list of exported to lua. This allows to do some scripting on lua query. One can think to DGA and data evasion.

PR builds:
- PR build: https://buildbot.openinfosecfoundation.org/builders/regit/builds/16
- PR pcaps: https://buildbot.openinfosecfoundation.org/builders/regit-pcap/builds/14

Hi, right. I was supposing the call to lua was doing it, but it is using pointer.