Bugfix #2705: if 'stderr=false' is set in phpunit.xml, it is ignored …

…and considered true.

src/TextUI/TestRunner.php

@@ -251,7 +251,7 @@ class_exists($arguments['printer'], false)) {
                 }
 
                 $this->printer = new $printerClass(
-                    isset($arguments['stderr']) ? 'php://stderr' : null,
+                    (isset($arguments['stderr']) && $arguments['stderr'] === true) ? 'php://stderr' : null,
                     $arguments['verbose'],
                     $arguments['colors'],
                     $arguments['debug'],