Applying patch from 'Justas Butkus' to DboSource

Fixes issues where reconnect could issue warnings related to
array_merge.  Fixes #1182

cake/libs/model/datasources/dbo_source.php

@@ -105,7 +105,7 @@ function __construct($config = null, $autoConnect = true) {
  * @param array $config An array defining the new configuration settings
  * @return boolean True on success, false on failure
  */
-	function reconnect($config = null) {
+	function reconnect($config = array()) {
 		$this->disconnect();
 		$this->setConfig($config);
 		$this->_sources = null;