this adds a completely new hash based mangling scheme

this adds a completely new hash based mangling scheme

the hash for this scheme is *much* larger (approximately 31 bits) and
the code is written to be very fast, correctly handling multibyte
while not doing any actual multi-byte conversions in the vast majority
of cases

you can select this scheme using "mangling method = hash2", although I
may make it the default if it works out well.
(This used to be commit bb173c1a7e2408ced967ebac40b5e3f852ccd3a1)