The body-lengths of sub-entities, like multipart messages, got counted
twice by mistake: once upon the end of the sub-entity and then again
upon the end of the top-level entity that contains all sub-entities.
The size of just the top-level entity is the correct one to use.
This commit switches UID hashing from md5 to a highway hash. It also
moves the salt value out of the file plugin - and makes it
installation-specific instead - it is moved to the global namespace.
There now are digest hash functions to make "static"
installation-specific hashes that are stable over workers available to
everyone; hashes can be 64, 128 or 256 bits in size.
Due to the fact that we switch the file hashing algorithm, all file
hashes change.
The underlyigng algorithm that is used for hashing is highwayhash-128,
which is significantly faster than md5.
The "orig_fuids", "orig_filenames", "orig_mime_types" http.log fields as
well as their "resp" counterparts are now limited to having
"HTTP::max_files_orig" or "HTTP::max_files_resp" entries, which are 15
by default. The limit can also be ignored case-by-case via the
"HTTP::max_files_policy" hook.
Fixes GH-289
