Delete importFile() and exportFile().  They always raised an
    exception, and there are no subclasses that provide an
    implementation.  I suspect they were decoys from the days
    before export/import was implemented on the Connection.
Remove UndoLogCompatible base class from DB, because it doesn't
    provide the undoLog() method needed to make it at all useful.
Deprecate all the cache_deactivate_after methods.
Replace list2dict with new dict.fromkeys() constructor.
Make imports global instead of local.
Add epydoc markup to DB class docstring.