Update to 20080615.2. Changes include:
- Remove the PID file just before dhcp6c actually exits.
- Set a DHCPv6 state keyword to an environment variable "REASON" which is passed to the client script when receiving a REPLY message instead of "NBI".
- Add a signal handler for SIGUSR1 to forcibly exit without releasing the obtained addresses.
- Add a new script event "EXIT", which is invoked when dhcp6c exits.