This removes a lot of complexity, since we basically just reserve
space on a retrieval of a label, and pass around strings. Two new
elements: (1) consumers of the API must now declare what label
elements they are interested in retrieving, or (2) rely on the default
provided in a new configuration file, mac.conf.
Approved by: re
Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories
