Restore -DWITH_SSL=system support for OpenSSL versions <= 0.9.8k.

MySQL 5.6.17 introduced support for block encryption modes and
initialization vectors for AES_ENCRYPT/AES_DECRYPT functions.  This
change broke backwards compatibility for older OpenSSL system
versions, as the ECB mode cipher there disagrees with recent OpenSSL
versions whether it need initialization vectors or not. As AES
functions directly check with OpenSSL for IV requirement and provide a
corresponding function signature, these differences result in SQL
incompatibilities.

Fixed by checking, for OpenSSL, whether ECB mode is in use whenever
OpenSSL reports required IV length > 0, and assuming IV length of zero
instead.

mysys_ssl/my_aes_openssl.cc

@@ -115,7 +115,8 @@ int my_aes_encrypt(const unsigned char *source, uint32 source_length,
   unsigned char rkey[MAX_AES_KEY_LENGTH / 8];
   my_aes_create_key(key, key_length, rkey, mode);
 
-  if (!cipher || (EVP_CIPHER_iv_length(cipher) > 0 && !iv))
+  if (!cipher || (EVP_CIPHER_iv_length(cipher) > 0
+                  && EVP_CIPHER_mode(cipher) != EVP_CIPH_ECB_MODE && !iv))
     return MY_AES_BAD_DATA;
 
   if (!EVP_EncryptInit(&ctx, cipher, rkey, iv))
@@ -157,7 +158,8 @@ int my_aes_decrypt(const unsigned char *source, uint32 source_length,
   unsigned char rkey[MAX_AES_KEY_LENGTH / 8];
 
   my_aes_create_key(key, key_length, rkey, mode);
-  if (!cipher || (EVP_CIPHER_iv_length(cipher) > 0 && !iv))
+  if (!cipher || (EVP_CIPHER_iv_length(cipher) > 0
+                  && EVP_CIPHER_mode(cipher) != EVP_CIPH_ECB_MODE && !iv))
     return MY_AES_BAD_DATA;
 
   EVP_CIPHER_CTX_init(&ctx);
@@ -212,6 +214,7 @@ my_bool my_aes_needs_iv(my_aes_opmode opmode)
 
   iv_length= EVP_CIPHER_iv_length(cipher);
   DBUG_ASSERT(iv_length == 0 || iv_length == MY_AES_IV_SIZE);
-  return iv_length != 0 ? TRUE : FALSE;
+  return iv_length != 0
+    ? (EVP_CIPHER_mode(cipher) != EVP_CIPH_ECB_MODE) : FALSE;
 }