! can: replace InetSocketAddress in HostConnectorSetup with hostname/port pair, fixes #394

Since two `InetSocketAddress` instances are equal if their hostnames resolve to the same IP/port (i.e. the address for "www.spray.io" and "spray.io" compare equal) the HTTP layer wasn't distinguishing properly between them.
This patch fixes this problem.
If you were relying on constructing an `HostConnectorSetup` with an `InetSocketAddress` you need to change your code to provide a host and port explicitly.