* plugin/forward: may Yield not block

Yield may block when we're super busy with creating (and looking) for
connection. Set a small timeout on Yield, to skip putting the connection
back in the queue.

Use persistentConn troughout the socket handling code to be more
consistent.
Signed-off-by: Miek Gieben <miek@miek.nl>

Dont do
Signed-off-by: Miek Gieben <miek@miek.nl>

* Set used in Yield

This gives one central place where we update used in the persistConns
Signed-off-by: Miek Gieben <miek@miek.nl>