test_dh.c includes scr_dh.c and still called sd_generate_safe_prime
without its new top_two argument, so dh.test.ts failed to compile. It
now passes false, as the DiffieHellman paths do, and a new case checks
generatePrime's search: the sizes and add forms with one possible
result, top-two-bit safe-prime starts, and checks above OpenSSL's round
count.