SessionHandlerPHP: Added missing () after session_id.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@85 44740490-163a-0410-bde0-09ae8108e29a

lib/SimpleSAML/SessionHandlerPHP.php

@@ -27,7 +27,7 @@ class SimpleSAML_SessionHandlerPHP extends SimpleSAML_SessionHandler {
 		 * to call session start. Otherwise the session is already
 		 * started, and we should avoid calling session_start().
 		 */
-		if(session_id === '') {
+		if(session_id() === '') {
 			session_start();
 		}
 	}