The afh_receiver, infrastructure.

The afh_receiver, infrastructure.

This adds a dummy implementation of the new afh_receiver which will
replace the streaming mode of para_afh.

It "receives" its input data from a local audio file rather than from
a network socket, but supports the same API as all other receivers. In
particular it provides a buffer tree node which feeds the chunks of
the audio file to any filter which is connected to that node. This
mechanism will be used by the para_play executable.

The afh receiver is not needed for para_audiod, so we link afh_recv.o
only to para_recv.