Use the same crc64 that we already use for the symbol table hash as
the perfect hash function prehash. We appear to get radically faster
convergence this way, and the crc64 is probably *faster*, since the
table likely to be resident in memory.
rand() in Perl can vary between platforms, so don't use it. Instead,
remove a completely pointless level of indirection (it introduced a
permutation which cancelled itself out) and provide a canned set of
random numbers for the rest. This guarantees we will always use the
same numbers.