Fake stdin for applications which exit on EOF.

Some applications, like MonetDB server, expect to read commands on
stdin.  If they read a keyword, usually "exit" or "quit" or if stdin is
closed, they will exit.

Such applications will typically work when run in a service context via
NSSM, as Windows will allocate a console window for them.  However, when
the service is configured to redirect stdout and/or stderr but not
stdin, the application will exit immediately because it will see no
input and think that the user closed stdin.

To deal with this situation we interpret an AppStdin value of "|" (a
single pipe character) as requesting a hack mode whereby we open a pipe
and pass the reading end to the application as the stdin handle.  We
never actually write anything to the writing end of pipe but simply keep
it around until the application exits or the service receives a stop
control.  Closing the pipe on receipt of a stop request may even be
sufficient to close the application gracefully without resorting to any
of the other stop methods.

As an aside, MonetDB server can be run in batch mode, wherein it does
not attempt to read from stdin at all.  The hack is not necessary for it
or other applications with similar functionality.

Thanks Bryan Senseman.