Use \refmodule when we say "use the XXX module instead".

For the whatsound module, point to sndhdr.

Doc/lib/libundoc.tex

@@ -220,14 +220,14 @@ func.func_name, co.co_firstlineno).
 
 \item[tb.py]
 --- Print tracebacks, with a dump of local variables (use
-\function{pdb.pm()} or \module{traceback} instead)
+\function{pdb.pm()} or \refmodule{traceback} instead)
 
 \item[timingmodule]
 --- Measure time intervals to high resolution (use
 \function{time.clock()} instead).  (This is an extension module.)
 
 \item[whatsound.py]
---- recognizing sound files
+--- Recognize sound files; use \refmodule{sndhdr} instead.
 
 \item[zmod.py]
 --- Compute properties of mathematical "fields"