This reverts commit e226e8c889.

This is a conveninece for nav-as-you-type mode.
With this program option, on pressing ^P, the filter is  executed as cmd.

-d is to show detail mode
-H is to show hidden files
-l is retired

The new location is ~/.config/nnn/.lastd

This may affect issue #227 but the defunct processes do not use any memory and exit when nnn exits. I guess that happens because of xdg-open using an intermediate script.

However, if we do not detach xdg-open, the child process is killed when the terminal is closed which is a severe problem.