NT file-permissions

[David Collier-Brown -- Customer Engineering]

A minor point on ACLs and permission bits: there is a U.S. government
standard for C1 and above, setting out what minimal capacities you
need from ACLs and what of these can be mapped to permission bits.

That means: we can represent some ACLs now everywhere, more on Unix
machines that have ACLS. We won't get everything, but we'll get the
security-relevant subset.

--dave