Make it possible to run tests on windows (with a little cygwin help)

Hi Gustavo,

This PR makes it actually possible to run tests in the native windows shell:

![image](https://cloud.githubusercontent.com/assets/1620265/4031208/ce4fdd60-2c64-11e4-974a-5a2c377c3786.png)

Making supervisor run on native windows is a lost cause. With a little extra finagling you can make it behave reasonably on Cygwin though.

Comments eagerly awaited :)
How does that even compile, when there's a S.Stop method in suite_test.go!?

Let's please have a single function here:

func kill(pid int, sig Signal) (err error) {
        return syscall.Kill(pid, sig)
}