we can return a (count of?) list of users, or fall back to the
user deletion descriptions.
+* Error reporting is inconsistent. We know what goes wrong, and then
+ errors bubble up, but where do they get reported? Are they fatal or
+ informational? Do we want later plugins to run of earlier ones
+ failed?
+
* Implement "mv".
Design:
the "mv" operation to the plugins. Some of them might have nothing
to do -- that's fine.
+ MAKE SURE WE DON'T OVERWRITE AN EXISTING USER!
+
* Add convenience methods (e.g. user_exists, domain_exists) that we
can use in the tests to check results.