playbin3 and playsink : Don't send seek event to only one sink
Submitted by Edward Hervey
Currently playsink only forwards seek events for one sink.
The problem is that with playbin3 we want to be able to support any number of sources and/or seek handlers.
Sending seek events to all sinks is trivial ... but there are quite a few elements out there that don't properly handle receive multiple seek (with the same seqnum) in a row.
I'm opening this bug to not forget about it.