This patch integrates the uplink sink feature of module-virtual-source into
the virtual source library, so that every virtual source can use it.
The patch also introduces latency handling and rewinding for the uplink sink.
Similar to the monitor source, the only useful definition of the latency
appears to be the negative of the master source latency. Rewinding will not
be possible in most situations, because the underlying memblockq is nearly
always empty.
module-combine-sink and module-suspend-on-idle required some changes to
deal correctly with this type of sink.
Analog to the virtual sink consolidation series, the common code of virtual sources
is moved to a library. The library adds support for fixed block size filters and
parameter changing. Rewinding has been dropped because virtual sources do not need
it.
