Make ResultSet buffer the statement results.

This will allow it to more easily implement serializable interface,
which will be important for caching results.

lib/Cake/ORM/ResultSet.php

@@ -85,6 +85,13 @@ class ResultSet implements Iterator {
  */
 	protected $_map;
 
+/**
+ * Results that have been fetched or hydrated into the results.
+ *
+ * @var array
+ */
+	protected $_results = [];
+
 /**
  * Constructor
  *
@@ -114,7 +121,7 @@ public function toArray() {
  * @return array|object
  */
 	public function current() {
-		return $this->_groupResult($this->_current);
+		return $this->_current;
 	}
 
 /**
@@ -188,7 +195,11 @@ protected function _calculateAssociationMap() {
  */
 	protected function _fetchResult() {
 		if ($this->_lastIndex < $this->_index) {
-			$this->_current = $this->_statement->fetch('assoc');
+			$row = $this->_statement->fetch('assoc');
+			if ($row !== false) {
+				$row = $this->_groupResult($row);
+			}
+			$this->_current = $row;
 			$this->_lastIndex = $this->_index;
 		}
 	}
@@ -198,10 +209,10 @@ protected function _fetchResult() {
  *
  * @return array
  */
-	protected function _groupResult() {
+	protected function _groupResult($row) {
 		$defaultAlias = $this->_defaultTable->alias();
 		$results = [];
-		foreach ($this->_current as $key => $value) {
+		foreach ($row as $key => $value) {
 			$table = $defaultAlias;
 			$field = $key;