Detect a format change in the payloader and post an element message.
Catch the format change element message in the client-source and use it
to update the format and possible formats in the source and source-outputs.
Add a global object that can be used to track outstanding fds for a
client. This can later also be used to limit the number of fds per
client.
Use this in the payloader to track fds. This makes it possible to track
the fds even when the client reconnects.
Set the client patch on the socket so that we can use it to track the
fds we sent to this client.
When the client disappears, release all outstanding fds.
Make sure we unref the source-input when it is removed.
When the source-input is removed, we should also unref the source. Do
this by adding the source as data for the source-input and unreffing it
when the source-input is freed.
