Bug 1050748 - [l10n] Cancel button is not localized when displaying matches from contacts in Dialer

This isn't the place to do this. It makes more sense to me to stick this in ```_initOverlay()``. It's not going to change once it's shown, and it doesn't need to be re-translated each time an item is added.
Also, this should be wrapped in a ```navigator.mozL10n.ready()``` call. It's exceedingly unlikely that l10n wouldn't load before this can be called, but there's no real reason not to do this.