mpm_winnt: Prevent the parent-child pipe from leaking into other

spawned processes, and ensure we have a /Device/null handle for
stdout when running as-a-service.

Backport: 568446


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@570306 13f79535-47bb-0310-9956-ffa450edef68