Add MariaDB Connector/C as a built-in alternative (v3.2.3).

vendor/MDBC/README

@@ -0,0 +1,15 @@
+This is LGPL MariaDB client library that can be used to connect to MySQL
+or MariaDB.
+
+This code is based on the LGPL libmysql client library from MySQL 3.23
+and PHP's mysqlnd extension.
+
+This product includes PHP software, freely available from
+<http://www.php.net/software/>
+
+If you want to be part of this development effort, you can discuss this at
+maria-developers@lists.launchpad.org.
+
+To report a bug you'll need to signup for an account at https://jira.mariadb.org
+
+The MariaDB team