fix #463 Focus on element inside Dialog widget not working on IE7

After dialog popup open, the $focus called from the callback it's not applied to the element.
fix #462 aria.widgets can be undefined

When no class in aria.widgets package is loaded, aria.widgets is undefined.
Before checking if aria.widgets.AriaSkin is defined, the existence of aria.widgets has to be checked first.
fix #461 PasswordField widget broken

Fixing a problem that is breaking the PasswordField widget inside sample page on ariatemplates.com. Adding also a widget test case.