or for using a diiferent initial working directory. We already
need to use a different working dir and this would allow us to
spawn multiple setup processes for parallel builds each with
their own working dir. Also, we want to be able to capture the
output of builds. At the moment our internal logging framework
is not capable of redirecting, but if we launch a process we
redirect its output to a file. This should be useful for build
reporting where we want logs for each individual package.