(Forward-port from D5 logic fixes) Updated _panels_page_update() to cope with the new use of the $panel_page->export property.

(Forward-port from D5 logic fixes) Updated panels_page_save_display() to cope with the new use of the $panel_page->export property.

Some refactoring, partially to accommodate changes suggested by douggreen. The basic context-loading problem has not yet been solved, however.

Save routines should now pretty much be functional. The problems appear to now pretty much be limited to context loading/generation at render time. It's not clear if the problem is with panels_page logic, the Panels engine, or some squirrely D6 changes.

'Write' functions - functions that are concerned with putting data in the database, or some other form of storage. The latter is the conceptual justification for putting export functions in here, too...which was originally done for practical reasons :)