This addresses the bug: https://github.com/arya/bluepill/issues/177

The soft 'exit' was not actually allowing the forked processes to end under Ruby 2.0.0.
This meant the parent got stuck on the waitpid - and the timeout eventually kicked in which invoked a stop - meaning it returned to the same code path. It was resulting in a large number of defunct/zombie processes being created.

This is resolved with a 'exit!' call instead.

Tested with Ruby 2 & 1.9.3 (running a unicorn pill file)