Make stumpish work on OpenBSD again

[catap]

This fixes regression which was introduced by #296

[catap]

@MIvanchev let move discussion here.

pgrep is part https://packages.debian.org/bookworm/procps on Debian which seems installed everywhere.

So, here a dramatic simplification of this function.

[MIvanchev]

I'm suggesting this variant with a fallback for the hopefully rare case that there isn't a pgrep.

stumpwm_pid ()
{
    if command -v pgrep 2>&1 >/dev/null; then
        STUMPWM_PID=$(pgrep stumpwm)
    elif [ -d /proc ]; then
        # Go up the process chain until we locate StumpWM's process using
        # the /proc virtual file system.

        local pid=$$

        while [ $pid -ne 1 ]
        do
            if [ "$(cat /proc/${pid}/comm)" = "stumpwm" ]; then
                STUMPWM_PID=$pid
                break
            else
                pid=$(cut -f 4 -d " " < /proc/$pid/stat)
            fi
        done
    fi

    if [ -z "$STUMPWM_PID" ]; then
        echo "StumpWM not found in the process tree, are you sure a graphical " 1>&2
        echo "session is running and StumpWM is your WM? If you think this is " 1>&2
        echo "a bug in stumpish, please report it." 1>&2
        echo 1>&2
        exit 1
    fi
}

[catap]

@MIvanchev here an updated PR.

[MIvanchev]

I tested this in both cases and works good on Void Linux.

[MIvanchev]

Thank you @catap !!!