Fix --error-output to be more like GNU m4.

GNU m4 --error-output is the same as -o despite the name.  It does NOT
affect warnings, error messages, and 'errprint' output so drop the
misguided bit of code that tried to freopen stderr without closing it
on failure.  Drop -e (which was our local invention) and make merge
--error-output with -o so that both set traceout.  Make trace_file()
preserve the old traceout on error and return error status so that the
caller can emit appropriate warning.

Do not yet support disabling tracing with an empty name, the rest of
the code is not ready, we don't do -o positionally and we don't have
`debugfile'.

(uwe)