Statically allocate arrays such as SEQ, SUBSEQ, D64, BJ64,
instead of using malloc.

In bsgs64 we compute b = 5^Q (mod p) for each p. This could be made more
efficient by precomputing y = 5^x where x is the largest divisor of Q such
that 5^x < p_min, then computing b = y^(Q/x) (mod p) for each p.

Remove any factor of 2 from r before checking whether r is a quadratic
residue with respect to p, and add (2/p) to the array of precomputed
residues.
