Allow early closing of sources and make them auto shutdown per default.

[back2dos]

Especially file descriptors must be closed.

If part of a file source is piped somewhere and the rest is never read, it should be possible to close the source (and thus the descriptor) without the need of piping the rest to a black hole or something.
To avoid open file descriptors from accumulating, sources that are idle for long enough (30secs?) should be automatically closed (there should be an opt-out for this of course).