Disable Dual EC DRBG.

Return an error if an attempt is made to enable the Dual EC DRBG: it
is not used by default.
(cherry picked from commit a4870de5aa)

crypto/rand/rand_lib.c

@@ -269,6 +269,14 @@ int RAND_init_fips(void)
 	DRBG_CTX *dctx;
 	size_t plen;
 	unsigned char pers[32], *p;
+#ifndef OPENSSL_ALLOW_DUAL_EC_DRBG
+	if (fips_drbg_type >> 16)
+		{
+		RANDerr(RAND_F_RAND_INIT_FIPS, RAND_R_DUAL_EC_DRBG_DISABLED);
+		return 0;
+		}
+#endif
+		
 	dctx = FIPS_get_default_drbg();
         if (FIPS_drbg_init(dctx, fips_drbg_type, fips_drbg_flags) <= 0)
 		{