openhip

during startup, hip should detect if a PID file already exists but the hip
process is not actually running, and print a message such as "warning:
removed stale PID file since process 12345 was no longer running"; current
behavior is just to exit with an error

also the location of /usr/local/var/run/hip.pid is slightly awkward,
probably OK to just store it in /var/run/hip.pid