Add error filename/number and context when available to ease debugging.

www/_include.php

@@ -53,7 +53,8 @@ function SimpleSAML_error_handler($errno, $errstr, $errfile = null, $errline = 0
     }
 
     // show an error with a full backtrace
-    $e = new \SimpleSAML\Error\Exception('Error '.$errno.' - '.$errstr);
+    $context = (is_null($errfile)?'':" at $errfile:$errline") . (is_null($errcontext)?'':" $errcontext");
+    $e = new \SimpleSAML\Error\Exception('Error '.$errno.' - '.$errstr . $context);
     $e->logError();
 
     // resume normal error processing