Add two sub-sections to the MAC Framework userland architecture section
of the Developer's Handbook: text on the APIs to access and manipulate
labels on objects, and a brief description of how labels may currently
be set on users using login.conf. This text could also use some more
work, but is probably an improvement over the previous lack of text.

Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories