Logging netty channel close is excessive

Excessive Netty logging when closing a connection from the browser. Discovered this when running the scala comet sample.

	[error] p.nettyException - Exception caught in Netty
	java.nio.channels.ClosedChannelException: null
		at org.jboss.netty.channel.socket.nio.AbstractNioWorker.cleanUpWriteBuffer(AbstractNioWorker.java:434) ~[netty.jar:na]
		at org.jboss.netty.channel.socket.nio.AbstractNioWorker.writeFromUserCode(AbstractNioWorker.java:129) ~[netty.jar:na]
		at org.jboss.netty.channel.socket.nio.NioServerSocketPipelineSink.handleAcceptedSocket(NioServerSocketPipelineSink.java:99) ~[netty.jar:na]
		at org.jboss.netty.channel.socket.nio.NioServerSocketPipelineSink.eventSunk(NioServerSocketPipelineSink.java:36) ~[netty.jar:na]
		at org.jboss.netty.handler.codec.oneone.OneToOneEncoder.handleDownstream(OneToOneEncoder.java:60) ~[netty.jar:na]
		at com.typesafe.netty.http.pipelining.HttpPipeliningHandler.handleDownstream(HttpPipeliningHandler.java:87) ~[netty-http-pipelining.jar:na]

Relates to a change we made (commit 5a35a47).