Return the 'legacy' not-quite-DCT matrix used by Sphinx

def s2dctmat(nfilt,ncep,freqstep):
    """Return the 'legacy' not-quite-DCT matrix used by Sphinx"""
    melcos = numpy.empty((ncep, nfilt), 'double')
    for i in range(0,ncep):
        freq = numpy.pi * float(i) / nfilt
        melcos[i] = numpy.cos(freq * numpy.arange(0.5, float(nfilt)+0.5, 1.0, 'double'))
    melcos[:,0] = melcos[:,0] * 0.5
    return melcos