note: forward declaration of 'cl

QT 4 support forward declaration

orward declaration is not supported as:

//#include <QtGui>
//class QCheckBox;
//class QLabel;
//class QLineEdit;
//class QPushButton;

must be replaced by:

#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QLineEdit>
#include <QCheckBox>
#include <QHBoxLayout>

QT4.82 support forward declaration, QT5.3 doesn't.