Do not call QWidget::show/hideEvent twice

Do not call QWidget::show/hideEvent twice

While handling events for Widgets and Windows in QWidgetWindow::event
makes sense for other events, it causes QWidget::show/hideEvent to be
called twice when handled like "the rest". Having that as one case here
seems to be the cleanest solution. Removing the call to showEvent from
QWidgetPrivate::show_helper (as proposed in the bug report) causes
autotests to fail and thus is not a viable option.

Additionally the expected result for the task221221 test for
QDoubleSpinBox was reverted to the Qt4 value as Qt4 behaviour was
restored.

Task-number: QTBUG-27199
Task-number: QTBUG-26424
Task-number: QTBUG-22565

Change-Id: I0ac42b09b1a7618de042d27aa5dd1b3d9f30f552
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Andy Shaw <andy.shaw@digia.com>