ACL / SD support

[Luke Kenneth Casson Leighton]

> 	Then we have to embed explicit access checks throughout Samba, which
> will destroy performance. 

no it won't.  

1) you really _should_ be doing such explicit access checks _anyway_.

2) such checks are only made on file-open and file-create.  microsoft
already has exactly this problem in NT, therefore they have designed
(read, munged) SMB to mitigate exactly this problem.

microsoft's already dealt with it, therefore, and solved it as best they
could, therefore we follow their lead (again) and get performance no worse
than theirs as a result.