* fork.cc (fork_parent): Don't issue errors if "somebody" has set the
PID_EXITED flag on a child. Don't close process handle if it has potentially
already been closed.
* pinfo.cc (winpids::add): Eliminate PID_ALLPIDS handling which was obsoleted
by previous changes.
* spawn.cc (av::fixup): Do win16 detection for .com files. Make sure that
buffer has been unmapped in all cases.