stream reassembly cleanup v2

Unify IDS/IPS stream reassembly code as much as possible.
General reassembly cleanups.

Prscript:
- PR build: https://buildbot.openinfosecfoundation.org/builders/inliniac/builds/102
- PR pcaps: https://buildbot.openinfosecfoundation.org/builders/inliniac-pcap/builds/102