Optimisation request

[Martijn Dekker]

I've noticed bash-5.0beta is quite a bit faster than bash-4.4 in running 
a lot of pure shell code. Good news.

One optimisation that isn't done yet: if a subshell function like
        f() (foo)

is used in a command substitution, it forks twice. I would like it if it 
could be optimised to eliminate the fork if the subshell function is the 
last command in the command substitution.

Thanks,

- M.