center frequency each time we allocate a new DDC/channel. Adds
support for broadcasting channel count change source events so that the
tuner can accurately convey sourced channel counts via tuner events.
Completes changeover of polyphase channel manager to support arbitrary
bandwidth channels. The new approach provides greater compatibility
across any tuner sample rates. Likewise, all decoders will have to be
updated to adapt to any channel sample rate, although channel bandwidths
will be at least 12.5 kHz and likely no more than 25.0 kHz, with a 2x
oversampling that produces channel sample rates in range 25.0 - 50.0
kHz.