only a few node references left

eventMouseClick.go

@@ -62,11 +62,11 @@ func doMouseClick(w int, h int) {
 		case widget.Checkbox:
 			if tk.Checked() {
 				log.Log(WARN, "checkbox is being set to false")
-				tk.node.State.Checked = false
+				tk.SetChecked(false)
 				tk.setCheckbox()
 			} else {
 				log.Log(WARN, "checkbox is being set to true")
-				tk.node.State.Checked = true
+				tk.SetChecked(true)
 				tk.setCheckbox()
 			}
 			me.myTree.SendUserEvent(tk.node)

node.go

@@ -57,3 +57,7 @@ func (tk *guiWidget) GridW() int {
 func (tk *guiWidget) GridH() int {
 	return tk.node.State.AtH
 }
+
+func (tk *guiWidget) SetChecked(b bool) {
+	tk.node.State.Checked = b
+}