bug#29225: Tramp backup-by-copying in a Converting ACL Invalid argument error on Windows 7

[Eli Zaretskii <eliz@gnu.org>]

> From: Shuguang Sun <shuguang@gmail.com>
> Date: Thu, 9 Nov 2017 16:24:39 +0800
> 
> Could we allow the user to set whether to copy ACl for certain type of files?

That should work automatically.

> Debugger entered--Lisp error: (file-error "Converting ACL" "Invalid argument"
> "c:/Users/user/HOME/.emacs.d/autosave/Rfiles/!drive_c!plink!!user@host!!!path!user!Ava!_mortality.R.~1~")
> 
>   set-file-acl
> ("c:/Users/user/HOME/.emacs.d/autosave/Rfiles/!drive_c!plink!!user@host!!!path!user!Ava!_mortality.R.~1~"
> "user::rw-\ngroup::rw-\nother::r--\n")
>   set-file-extended-attributes
> ("c:/Users/user/HOME/.emacs.d/autosave/Rfiles/!drive_c!plink!!user@host!!!path!user!Ava!_mortality.R.~1~"
> ((acl . "user::rw-\ngroup::rw-\nother::r--\n") (selinux-context nil nil nil nil)))
>   backup-buffer-copy("/plink:user@host:/path/user/Ava/_mortality.R"
> "c:/Users/user/HOME/.emacs.d/autosave/Rfiles/!drive_c!plink!!user@host!!!path!user!Ava!_mortality.R.~1~"
> 436 ((acl . "user::rw-\ngroup::rw-\nother::r--\n") (selinux-context nil nil nil nil)))

This seems to indicate that Unix-style ACLs are passed to native
Windows ACL functions, which won't work.  Michael, could you please
look into this?  I'd expect ACLs derived from remote files never to be
used on local files.

Thanks.