vcl: Add sink effect (QStyle::State_Sunken) to menubar on KDE

A selected menubar item of cleanlooks, gtk+ and plastique styles
becomes closer to standard looks by passing QStyle::State_Sunken
with QStyle::CE_MenuBarItem to QStyle::drawControl(). It is
currently not documented on QT developmet resources. But these
styles interpret that.

Change-Id: Ic7835bf0bf7af374ebdf8330d15b462d056de8a5
Reviewed-on: https://gerrit.libreoffice.org/4017Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>

vcl/unx/kde4/KDESalGraphics.cxx

@@ -300,6 +300,9 @@ sal_Bool KDESalGraphics::drawNativeControl( ControlType type, ControlPart part,
             if ( nControlState & CTRL_STATE_ROLLOVER )
                 option.state |= QStyle::State_Selected;
 
+            if ( nControlState & CTRL_STATE_SELECTED ) // Passing State_Sunken is currently not documented.
+                option.state |= QStyle::State_Sunken;  // But some kinds of QStyle interpret it.
+
             draw( QStyle::CE_MenuBarItem, &option, m_image,
                   vclStateValue2StateFlag(nControlState, value) );
         }