This patch provides the ability to filter audit messages based on the
elements of the process' SELinux context (user, role, type, mls sensitivity,
and mls clearance).  It uses the new interfaces from selinux to opaquely
store information related to the selinux context and to filter based on that
information.  It also uses the callback mechanism provided by selinux to
refresh the information when a new policy is loaded.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>