New function for shuffling associative arrays

There is a problem at the standard (STL) realization: it doesn't work with assoc arrays, so [0 => 123, 5 => 123] is transformed into [0 => 123, 1 => 123].

`Arr::shuffle_assoc` saves keys.

~dev_rating/system/classes/Kohana/Arr.php

@@ -10,7 +10,22 @@
  */
 class Kohana_Arr {
 
-	/**
+    public static function shuffle_assoc($list) {
+        if (!is_array($list))
+            return $list;
+
+        $keys = array_keys($list);
+        shuffle($keys);
+
+        $random = [];
+        foreach ($keys as &$key) {
+            $random[$key] = $list[$key];
+        }
+
+        return $random;
+    }
+
+    /**
 	 * @var  string  default delimiter for path()
 	 */
 	public static $delimiter = '.';