Use DEBUG or NODE_DEBUG to enable logging
Setup all workers with _control and birth time
Test worker, add support for exit by erroring
Test worker, add support for commands in env
Throttle worker restarts after an abormal exit
Test reorganized into categories, and size reset

There are getting to be too many of them, I might have to split them
soon, which will be easier if they are broken into sections.

Reorganizing tests revealed a dependency on size being undefined at
start of a test, which requires size to be set to undefined on stop.
This particular test used to run before master was ever run, so
master.size was always undefined. The test is arguably wrong, but
I prefer master state to be reset on stop, so I made the test pass.
Add restart command, to restart all workers