Interface for cancelling ChoiceEdit changes is inconsistent with the rest of Launchpad

1. Click on the status or importance value for any bug report (such as this one).
2. Close the menu of status or importance values without making any changes.

What happens: The interface for cancelling the change is a little grey disabled-looking (✖) button at the top right corner of the overlay.

What should happen: The control for cancelling the change should be consistent with the interface for cancelling other actions in Launchpad. This means either a red non-disabled-looking (✖) button together with a green (✔) button at the bottom right corner of the overlay, or having no interface for cancelling except for closing the overlay when you click outside it (as used in real menus).

As with bug 399231, bug 399233, and bug 399236, this could be fixed by using a real <select> menu instead of an HTML+CSS overlay, because people are already familiar with how real <select> menus open and close.