Bug1067 v1.1

Here's an implementation of HTTP memcap. It puts a memcap on all allocations made for HTP by using dedicated allocation function. Two last commits implements some counters (memuse and memcap hit).

PR builds:
- PR build: https://buildbot.suricata-ids.org/builders/regit/builds/88
- PR pcaps: https://buildbot.suricata-ids.org/builders/regit-pcap/builds/27

Ticket: https://redmine.openinfosecfoundation.org/issues/1067