[2.0.2] dns txt bug1158 v0.1

Bug https://redmine.openinfosecfoundation.org/issues/1158

Prscript:
- PR build: https://buildbot.suricata-ids.org/builders/inliniac/builds/302
- PR pcaps: https://buildbot.suricata-ids.org/builders/inliniac-pcap/builds/219