Previously we would have forced all users to use nocase with http_host
keywords(since the hostname buffer is lowercase).
We now error out on sigs that has nocase set with http_host set. Also if
the http_host pattern or http_host pcre has an uppercase character set, we
invalidate such sigs. Unittests also updated to reflect the above change.
All fp id assignment now happens in one go.
Also noticing a slight perf increase, probably emanating from improved cache
perf.
Removed irrelevant unittests as well.