bug#34488: Add sort --limit, or document workarounds for sort|head error messages

[Paul Eggert]

You make good points about nohup. Still, it's too bad that we'd have to add a 
new command for such a trivial thing.

Perhaps it'd be better to overload 'env' instead, as you proposed earlier. After 
all, env is already being used for another little environmental thing (namely 
changing directories), and if we find future needs for yet other little things 
(running with a different umask, say) we can put them under 'env' as well.