reversed layerup/layerdown direction on shift-mousewheel

gviz.py

@@ -25,8 +25,8 @@ class window(wx.Frame):
     def zoom(self, event):
     	z=event.GetWheelRotation()
     	if event.ShiftDown():
-    		if z > 0:   self.p.layerup()
-    		elif z < 0: self.p.layerdown()
+    		if z > 0:   self.p.layerdown()
+    		elif z < 0: self.p.layerup()
     	else:
     		if z > 0:   self.p.zoom(event.GetX(),event.GetY(),1.2)
     		elif z < 0: self.p.zoom(event.GetX(),event.GetY(),1/1.2)