Use rpid in the daemon and the scheduler to append the PID of their
common login process to the named pipe so daemons and schedulers in
other sessions won't conflict with one another.
It looks like if the daemon is started in the .xinitrc, its PID
can change once the X session is fully started. This will cause
long-running schedulers that were started along with the daemon
to not find it and exit soon after the session is started. So have
the schedulers check for the newest daemon instance each time they
are about to send it a signal. This is probably more efficient than
before when we were getting the PID once when the scheduler starts,
because the scheduler would validate that the PID still referred to
a daemon each time it sent a signal. Getting the PID replaces that
validation check, and may actually be faster.
