fix compile for Qt 4

Change-Id: Ifa6c3857e82e7fe8facf6c2437ce01134ee0615e
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>

src/plugins/qmlprojectmanager/qmlapp.cpp

@@ -35,6 +35,7 @@
 #include <utils/fileutils.h>
 #include <utils/qtcassert.h>
 
+#include <QDebug>
 #include <QDir>
 #include <QTextStream>