Some improvements for the Import pages

Good changes all. All of these apply to the panels core client modules, not the API itself, so this isn't a concern here. But it's relevant, so let's consider it a note, and forgive me if you already know this: we have to be wary about changing the default text on any submit buttons in the core API, as doing so constitutes an actual API change. Since the button text determines the contents of $_POST['op'] on form submission and we don't have $form_state in D5, client modules are often left with nothing except $_POST sniffing to determine the state of the form. If we change the default op value on folks, it could break their modules in a very annoying, very difficult to find kind of way.

At this point there's a plethora of issues with form descriptions, which is actually something systemic: barring some crazy annoying implementations of hook_form_alter(), when client modules implement one of the core API panels_edit* functions have no control over what appears in the widget descriptions; even the support for form submission buttons (via $finish) is sketchy in places. Consequently, we're kinda forced to use these incredibly bland, generic widget descriptions, and in places, merlin accidentally wrote descriptions that are specific to one or another panels core client module instead of a generic one.

Blah blah blah. Patch committed :)