Update to wavread.m and wavwrite.m

On  7-Oct-2007, Michael Zeising wrote:

| I've currently noticed that the sample scaling in my WAV functions is 
| wrong and causes asymmetries and DC components (thanks to Denis 
| Sbragion). I've attached an updated version of them and I hope you can 
| include them into the distribution of octave. Thanks in advance!

Please send context diffs relative to the version you started with to
make your modifications.  That way, we won't lose any changes that may
have been made to the versions of these functions that are already in
Octave.

Please also use the [email protected] list for sending patches to
functions that are already a part of Octave.  The sources list was
originally intended as a place to post add-on functions to Octave and
is mostly dead now that Octave Forge exists.

Thanks,

jwe