* setfacl.cc (modacl): Move recomputing mask into new function.
(check_got_mask): New function checking if mask is in input.
(recompute_mask): New function to recompute mask.
(addmissing): Align mask computation to Linux setfacl.
(setfacl): Call check_got_mask and recompute_mask on Set, Delete and
Modify actions.
(usage): Rename --substitute to --set.
(longopts): Add --set option.
* utils.xml (setfacl): Rename --substitute to --set.
* new-features.xml (ov-new2.4): Rephrase setfacl changes.
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>