Add support for primality checking

Add support for primality checking

Project Wycheproof's primality_tests.json contain a set of 280 numbers
that trigger edge cases in Miller-Rabin and related checks. libcrypto's
Miller-Rabin test is known to be rather poor, hopefully we will soon see
a diff on tech that improves on this.

This extends the Go test in the usual way and also adds a perl script
that allows testing on non-Go architectures.

Deliberately not yet linked to regress since the tests are flaky with
the current BN_is_prime_ex() implementatation.