preserve_uidgid is described in the manual, but is not implemented

[Andrew V. Samoilov]

This feature should be usefull for system administrators and even 
documented in the mc.1, but it is commented out in setup.c and does not 
implemented in filegui.c and fileopctx.c.

Is it worth the trouble to implement this feature? (about 10 lines in 
the 3 files).
-- 
Regards,
Andrew V. Samoilov