LimitClause: offset compatibility. Fixes FaaPz#47

Use the de-facto standard LIMIT n OFFSET m syntax instead of MySQL-specific LIMIT n,m.

src/PDO/Clause/LimitClause.php

@@ -30,7 +30,7 @@ public function limit($number, $offset = null)
         }
 
         if ($offset >= 0) {
-            $this->limit = intval($offset).' , '.intval($number);
+            $this->limit = intval($number).' OFFSET '.intval($offset);
         } elseif ($number >= 0) {
             $this->limit = intval($number);
         }