fix #401 HashManager works correctly in IE7 even after a domain change

In order to provide support for back and forward in hash-based navigation in Internet Explorer 7, class `aria.utils.HashManager` creates a hidden iframe to open and close each time the history has to be populated with an entry.

When the `document.domain` is changed, IE7 denies access to some global variables of the iframe, unless the `document.domain` is updated inside the iframe, too. In order to notify that document.domain has been explicly set, variable `Aria.domain` has to be set to the same value.