2 is a prime

PR: 1266

crypto/bn/bn_prime.c

@@ -258,7 +258,8 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
 
 	/* first look for small factors */
 	if (!BN_is_odd(a))
-		return 0;
+		/* a is even => a is prime if and only if a == 2 */
+		return BN_is_word(a, 2);
 	if (do_trial_division)
 		{
 		for (i = 1; i < NUMPRIMES; i++)