Update the PMease wiki to describe how the Stop Build feature works. From an e-mail conversation with Robin:
QB interrupts all step threads in JVM, and upon this interruption, the step will send SIGTERM to all the forked child processes. And if some of them does not exit in 5 seconds, QB calls kill -9 to forcibly kill those child processes.

In addition to this verbiage, a warning that describes scenarios in which Quickbuild will not be able to stop a step. Such as executing a command remotely over SSH (only the SSH session would be controlled by QB), and scenarios in which the PID is detached from the QB PID tree and no longer tracked by a PID that QB has control over. Additionally, links to the Unix Signals wikipedia page (https://en.wikipedia.org/wiki/Unix_signal) and a reference to zombie processes should be noted.

While a lot of this is outside of the scope of what Quickbuild should be required to cover, it would go a long way to eliminate confusion and frustration for this feature of Quickbuild.