stream updates v1.6

Improve GAP handling, reduce memory usage. Add (hardcoded) protocol detection cut offs.

Rebase of https://github.com/inliniac/suricata/pull/942

Prscript:
- PR build: https://buildbot.suricata-ids.org/builders/inliniac/builds/276
- PR pcaps: https://buildbot.suricata-ids.org/builders/inliniac-pcap/builds/194