A list of PAS-related issues to resolve:

• IUserEnumeration should return empty list if it doesn't recognize the search criteria
• PlonePAS's IUserIntrospection should disappear
• Define new plug-in return codes to differentiate btn different types of failures
• Clarify behaviour w.r.t the keywords of IUserManager's doChangeUser method, how does this relate to property management?
• Resolve inconsistency btn PlonePAS IUserManager's canDelete() and doDeleteUser() methods (canDelete only checks one plug-in, doDeleteUser will try them all)