Return may be smaller than zero
Client retransmits don't get sent to a virtual server.
assert that we don't open sockets to virtual servers
Mark NO_CHILD_THREAD on forcible STOP_PROCESSING
Fix handling of proxying to virtual servers.  Fixes #596

The downside is that there isn't really any parent/child
relationship between the real request and the fake one.
So if the fake one blocks for 60s, the real one will be told
to stop, and the fake one with happily continue.

We'll need a separate commit to fix that issue.