Restore XTreeView functionality

I thought Qt5 had fixed this behaviour 'bug', but apparently not. So we
still need XTreeView - for Qt5 also.

client/xtreeview.h

@@ -24,11 +24,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>
 
 #include <QMouseEvent>
 
-#if 0 // FIXME: Test and remove
-#if QT_VERSION >= 0x050000
-#error "Do we even need this anymore?"
-#endif
-
 class XTreeView : public QTreeView
 {
 public:
@@ -46,9 +41,6 @@ private:
         QTreeView::mousePressEvent(event);
     }
 };
-#else
-typedef QTreeView XTreeView;
-#endif
 
 #endif