Properly daemonize the mail_room process

The old invocation only worked by accident because we have a '&'
somewhere in the init script for expediency. When ran from a terminal,
the mail_room daemon process ended up in the session of the terminal.
This commit adds a small wrapper that tries to do the textbook
daemonization steps (double fork, setsid etc.) while also taking
care that the pidfile is written before the 'start' process exits.

bin/daemon_with_pidfile

+#!/usr/bin/env ruby
+# daemon_with_pidfile
+#
+# Daemonize, write a pidfile, and exec the remainder of the command line.
+
+def main(pidfile, cmd)
+  if middle_pid = Process.fork
+    # outer process
+    # Do not exit the outer process before the middle process finishes
+    Process.waitpid(middle_pid)
+    exit $?.exitstatus
+  end
+
+  if final_pid = Process.fork
+    # middle process
+    open(pidfile, 'w') { |f| f.puts final_pid }
+    exit
+  end
+
+  # Standard daemon things: become session leader, ignore SIGHUP, close stdin.
+  Signal.trap("HUP", "IGNORE")
+  Process.setsid
+  IO.new(0).close
+
+  exec(*cmd)
+end
+
+if ARGV.count < 2
+  abort "Usage: #$0 pidfile command [args...]"
+end
+
+pidfile = ARGV.shift
+main(pidfile, ARGV)

bin/mail_room

@@ -19,9 +19,7 @@ get_mail_room_pid()
 
 start()
 {
-  bundle exec mail_room -q -c $mail_room_config >> $mail_room_logfile 2>&1 &
-  PID=$!
-  echo $PID > $mail_room_pidfile
+  bin/daemon_with_pidfile $mail_room_pidfile bundle exec mail_room -q -c $mail_room_config >> $mail_room_logfile 2>&1
 }
 
 stop()