Fix for issue #8

I haven't found anything that this PR breaks *yet*. Environment variables, stdio and current working directory appear to stay in-tact. It's possible that there is something else this could break, but for our use case, we can't use win-spawn at all without the ability to kill processes.

If this can't be merged, I'll just continue to maintain a one-off fork to resolve the issue for our internal stuff.

Thanks again!