Fix bug 1110 - Same PID for patterns with different CASE flags

Fixes bug 1110 https://redmine.openinfosecfoundation.org/issues/1110 and addresses review comments from PR 842 and PR 843, which this PR replaces. Now using SCMemcasecmp() instead of strncasecmp().

Now also using memcpy_tolower(), which was moved into util-memcpy.h to be shared with all the AC MPM code.

Removes the need for the case_state on patterns in MPM.

Passes PR scripts:
  https://buildbot.suricata-ids.org/builders/ken-tilera/builds/126
  https://buildbot.suricata-ids.org/builders/ken-tilera-pcap/builds/60