bug#8391: chmod setuid & setguid bits

[Bruno Haible]

Ondrej Vasik cited Paul Eggert:
> > recommend leading '@' for future scripts.

This use of '@' in a mode string conflicts with the use of '@' on
MacOS X 10.5 and newer to designate "extended attributes" (like
quarantine information on MacOS X 10.7).

$ /bin/ls -l /etc/ntp.conf
-rw-r--r--@ 1 root  wheel  27 Apr  5  2008 /etc/ntp.conf

$ /bin/ls -l@ /etc/ntp.conf
-rw-r--r--@ 1 root  wheel  27 Apr  5  2008 /etc/ntp.conf
        com.apple.TextEncoding  15 

You can see that both in the mode string (-rw-r--r--@) as well as among the
'/bin/ls' command-line option, the '@' has the meaning "extended attributes".

Having GNU coreutils interpret "@rw-r--r--" in a completely different way would
be counterintuive and confusing.

Bruno