Fixed a needless conversion to byte and string.

Added comment to show the purpose.
Added testcase.

node.go

@@ -66,9 +66,11 @@ func (this *Node) GetValue() string {
 	return res
 }
 
+// SetValue sets the value of the node to the given parameter.
+// It deletes all children of the node so the old data does not get back at node.GetValue
 func (this *Node) SetValue(val string) {
 	t := NewNode(NT_TEXT)
-	t.Value = string([]byte(val))
+	t.Value = val
 	t.Parent = this
 	this.Children = []*Node{t} // brutally replace all other children
 }