Unitech/pm2 — pull request #229 by bpostlethwaite (2013-12-22 18:37:07+00:00)
Title: add pm2_id to external msgs to link msg to sending process

It is useful to be able to link messages sent on the external bus to a particular process - especially in cluster mode where a script does not have any internally distinguishable state. Also useful coupled with [this feature](https://github.com/Unitech/pm2/pull/214) allowing 2-way messaging over the PM2 subsystem.