When a BuildML editor is saved, run emptyTrash() on the file to remove
dead package members.
Add a new flag to the "deletePath" and "deletePathTree" methods to
optionally remove the path accesses from any actions that refer to the
deleted path. If this flag is false, the deletion is disallowed.
Automatically enable "fast DB access mode" for all undo/redo operations,
and ensure that sub (nested) enables/disables are ignored. This causes
large undo/redo operations to be done as quickly as possible, only
committing the database at the end of the whole operation.