Fix for the tabs with no close-boxes

[scripting]

I never seem to have time to get to the bottom of where the closeboxless tabs come from , so I swatted it from the other side.

Now, periodically, Drummer looks at each tab, and any hidden closeboxes are made visible.

For future reference, the problem happens when you load an instant outline and there's an error reading the OPML file over the net. It never gets to the code that makes the closebox visible.

Onward!