Operations on the ajax popup overlay should be managed by a manager

Use http://tracker.phpbb.com/browse/PHPBB3-11280 to obtain an error.

There are two requests made. The first one suceeds, the second one fails. The first requests initiates the popup overlay with automatic hiding. The second one is supposed to show the overlay until the user dismisses it.

What happens is the overlay with the error is automatically hidden.

This should not happen. Show/hide requests should be issued via a manager object. The manager must keep track of what is currently displayed in the overlay. If an error is requested to be displayed, any outstanding pending hides are to be canceled.