More robust signaling of dyno processes

Change effective on 01 May 2012

When stopping or restarting dynos, unix signal SIGTERM now goes to all processes in the dyno, not just the first process. This provides a graceful shutdown for Resque workers and Play Framework apps (among others), avoiding spurious R12 (Exit timeout) errors.

During a brief transition period, you can revert to the old behavior with the sigterm-all Heroku Labs feature.