only use widget flag for existing Qt version
only use widget flag for existing Qt version

WA_LockPortraitOrientation has been introduced with 4.7.2 and
hence cannot be used with earlier Qt versions.

Reviewed-by: owolff

qtproject/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,KDE/android-qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility