Fixed compiler error in itemWithLabel:action:

When newItem below is of type id, then setAction can match a number of selectors. E.g. UIMenuItem action property which takes SEL types. This fix changes newItem to type RIButtonItem so compiler can marshal parameters for method call correctly. See http://www.cocoawithlove.com/2011/06/big-weakness-of-objective-c-weak-typing.html

	id newItem = [self itemWithLabel:inLabel];
  	[newItem setAction:action];