Fix missing tabfocus with manhattanstyle

I added a new focus rect for combo boxes
with manhattan style. To reduce the visual
impact I follow the same policy we use on
windows where we do not show the focus rect
unless it is called upon by tabfocus.

src/plugins/coreplugin/navigationwidget.cpp

@@ -376,6 +376,7 @@ NavigationSubWidget::NavigationSubWidget(NavigationWidget *parentWidget)
 
     m_navigationComboBox = new NavComboBox(this);
     m_navigationComboBox->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
+    m_navigationComboBox->setFocusPolicy(Qt::TabFocus);
     m_navigationComboBox->setMinimumContentsLength(0);
     m_navigationWidget = 0;