Fix fork issue

jackeventcmd forks before launching commands and then calls system. This
means that two processes are launched for each command; a jackeventcmd
fork and sh -c. The process forked by jackeventcmd does not terminate
properly. The following patch changes jackeventcmd to fork once and
execute sh -c. The forked process exits correctly.

https://github.com/gentoo-root/jackeventcmd/issues/1