Merge branch 'develop' of https://github.com/PHPOffice/PHPExcel into calcEngine

Conflicts:
	Classes/PHPExcel.php
	Classes/PHPExcel/Worksheet.php

Classes/PHPExcel.php

@@ -177,6 +177,14 @@ class PHPExcel
 		return $this->_calculationEngine;
 	}	//	function getCellCacheController()
 
+    /**
+     * Code to execute when this worksheet is unset()
+     *
+     */
+	function __destruct() {
+		$this->disconnectWorksheets();
+	}
+
     /**
      * Get properties
      *