Check for running daemons before a custom start_cmd is executed

[erdgeist_erdgeist.org]

Summary

Currently rc scripts implementing their own start_cmd do not enjoy the benefits of rc.subr's own check for rc_pid.

This leads to around a third of ports with such a start_cmd not to check for the process at all and two thirds of ports to re-implement this check (sometimes wrongly).

This patch moves the check for rc_pid to before ${rc_arg}_cmd is executed.

[feld]

This solves an annoyance for me. Thanks for doing this!