native posix permissions

[Luke Kenneth Casson Leighton]

> Actually, Samba will send mapped ACLs always if the nttrans
> GetSecDesc call is made, and UNIX perms always if the modified
> trans2 call is made, it's how the client asks that's important.

you got a format for the structures / info levels, i can plug it into
cliffs/idl/trans2.struct and get code pretty much immediately.

with about a days' work i can get you a client-side implementation, too.