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.
With this patch the model is:
- "print" cleans the data so that non-printable characters get
escaped. This is not necessarily reversible.
- to print in a reversible way, one can go through
escape_string(); this escapes backslashes as well to make the
decoding non-ambigious.
- Logging always escapes similar to escape_string(), making it
reversible.
Compared to master, we also change the escaping as follows:
- We now only escape with "\xXX", no more "^X" or "\0". Exception:
backslashes.
- We escape backlashes as "\\".
- There's no "alternative" output style anymore, i.e., fmt() '%A'
qualifier is gone.
Baselines in testing/btest are updated, external tests not yet.
Addresses BIT-1333.
