SSE 4.2 memcmp: don't read beyond var boundary

In the SSE 4.2 SCMemcmpLowercase implementation, there would be a
_mm_load_si128 of a 2 byte array. However, _mm_load_si128 loads
16 bytes, causing it to read beyond the var. I don't think this lead
to crashes, as it was a static var, but clangs ASAN complained about
it.
http: add meta-field-limit option

The meta-field-option allows for setting the hard limit of request
and response fields in HTTP. In requests this applies to the request
line and headers, not the body. In responses, this applies to the
response line and headers, not the body.

Libhtp uses a default limit of 18k. If this is reached an event is
raised.

Ticket 986.
flow: aligned flow balance structures (used by autofp) to CLS to reduce false sharing
build-info: add a nicer way of printing atomics support