PR: 70

(by using new BN_pseudo_rand_range function)

Bleichenbacher's DSA attack.  With this implementation, the expected
number of iterations never exceeds 2.

New semantics for BN_rand_range():
BN_rand_range(r, min, range) now generates r such that
     min <= r < min+range.
(Previously, BN_rand_range(r, min, max) generated r such that
     min <= r < max.
It is more convenient to have the range; also the previous
prototype was misleading because max was larger than
the actual maximum.)

New function BN_pseudo_rand().
Use BN_prime_checks_size(BN_num_bits(w)) rounds of Miller-Rabin when
generating DSA primes (why not use BN_is_prime()?)