io: upgrade to Akka IO as of 2013-05-01
Merge branch 'akka-io-update'

Conflicts:
	spray-io/src/main/scala/akka/io/SelectionHandler.scala
	spray-io/src/main/scala/akka/io/Tcp.scala
	spray-io/src/main/scala/akka/io/TcpConnection.scala
	spray-io/src/main/scala/akka/io/TcpListener.scala
	spray-io/src/main/scala/akka/io/UdpListener.scala