Fix the execution context for widget attributes specified as macros

We need to ensure that variables in the tree up to this point are
accessible when we render the macro text.

core/modules/widgets/widget.js

@@ -218,7 +218,7 @@ Widget.prototype.computeAttributes = function() {
 			value = self.wiki.getTextReference(attribute.textReference,"",self.getVariable("currentTiddler"));
 		} else if(attribute.type === "macro") {
 			var text = self.getVariable(attribute.value.name,{params: attribute.value.params});
-			value = self.wiki.renderText("text/plain","text/vnd.tiddlywiki",text);
+			value = self.wiki.renderText("text/plain","text/vnd.tiddlywiki",text,{parentWidget: this});
 		} else { // String attribute
 			value = attribute.value;
 		}