Comment 3 for bug 162502

Seperate change that addresses the same problem on windows, by detaching the child process from the parent console. I don't think this should cause the sort of problems (like bug 40508) that setting the process group did on nix, as prompts are currently broken anyway (as in 414743). However, it does cause a change in how the progress is displayed - it loses the 'bar' bit - for reasons I haven't had a chance to try and understand yet.