Bug 1078295 - Add transitions to menus in SMS. r=steveck

Got it, added tests for hiding after transition. I haven't explicitly tested for the visible class as I consider that an internal implementation detail (and I'm not sure what testing for the class explicitly would achieve as opposed to testing for the menu's attachment to the DOM).
As an aside, it ends up the option_menu test for hiding was broken, as it was trying to check the parent of the menu object instead of its form element.