Improve performance of MHR script, addresses BIT-1139.

The MHR script involves a "when" statement which can be expensive due to
the way it clones frames/vals.  In this case, the fa_file record is
expensive to clone, but this change works around that by unrolling only
the necessary fields from it that are needed to populate a Notice::Info
record.  A drawback to this is that the full fa_file or connection
records aren't available in the Notice::Info record when evaluating
Notice::policy hooks for MHR hit notices (though they can possibly be
recovered by using e.g. the lookup_connection() builtin_function).
Merge remote-tracking branch 'origin/fastpath'

* origin/fastpath:
  Derive results of DNS lookups from from input when in BRO_DNS_FAKE mode.

BIT-1134 #closed
Updating submodule(s).

 [nomail]
Merge remote-tracking branch 'origin/fastpath'

* origin/fastpath:
  update submodules
  Fix compile errror on freebsd - defines have to be moved up due to header dependencies.
Updating submodule(s).

 [nomail]
Change the standalone sumstats mode to work incrementally.
Now the standalone sumstats works even if Bro is shutting down by blocking.
Merge remote-tracking branch 'origin/topic/seth/sumstats-standalone-fix'

* origin/topic/seth/sumstats-standalone-fix:
  Now the standalone sumstats works even if Bro is shutting down by blocking.
  Change the standalone sumstats mode to work incrementally.
Merge remote-tracking branch 'origin/topic/jsiwek/faster-mhr'

* origin/topic/jsiwek/faster-mhr:
  Improve performance of MHR script, addresses BIT-1139.
Update instructions on how to build Bro docs

Also added a note in the main docs about building the Bro docs.