Separate notification from deletion in repository-handlers.

* Add NotifyDone() to all repository-attribute handlers and invoke that
  to notify any listeners.
* Unify deletion to a single implementation of Delete() in the base
  class. Before, the root handler for a repository didn't do that, but
  just triggered the notification.
Fix keeping of package info during repository update.

* actually write the package info read from the repository, not the one
  from the package, as the latter is missing the checksum