Exit race in otp supervisor

[iliastsi]

(For a brief explanation of what's going on see https://gist.github.com/beerriot/28258f2a44fc482016b1/revisions)

What's going on:
Child terminates (therefor monitor/2 returns noproc) but the message 'EXIT' arrives to it's father later on. Concuerror cannot handle this right now.

How to:
We have to trace the links between registered processes and send 'EXIT' messages as part of a new preemption action (differentiate exit and message passing as two distinct actions).