Do not destroy session, because Zend_Session_SaveHandler_DbTableTest::testSessionSaving needs it

tests/Zend/Session/SessionTest.php

@@ -1100,6 +1100,8 @@ class Zend_SessionTest extends PHPUnit_Framework_TestCase
         $sid = Zend_Session::getId();
 
         // We don't need the session any more, clean it up
+        //but we don't to want to destroy it completely, while other tests can start
+        Zend_Session::$_unitTestEnabled = true; 
         Zend_Session::destroy();
         foreach ( $sessionCharSet as $subdir ) {
             @rmdir($sessionStore . DIRECTORY_SEPARATOR . $subdir);