[preview] xbits v6.4

"xbits" implementation: as flowbits, but track by ip_src, ip_dst and ip_pair
For the the latter it adds an ip_pair tracking table.
Also has the 'hostbits' support from #1263 

Prscript:
- PR build: https://buildbot.openinfosecfoundation.org/builders/inliniac/builds/100
- PR pcaps: https://buildbot.openinfosecfoundation.org/builders/inliniac-pcap/builds/100