This provides some discovery capabilities to radiod and redirectord, so
that in most cases fewer command-line options are required for operation.

Split networking is where nodes communicate among themselves on a
private network (for example when behind a NAT infrastructure). This
change adds the --internal-ip option to radiod, that advertises a
separate IP for internal communication.

The only thing we need from ghost is the GZIPHandler. The
gorilla/handlers package has a CompressHandler, and much fewer
dependencies. Also, add a test that attempts a request with
an Accept-Encoding: deflate header.

RemoteAddr again.

Also removed some unnecessary duplication of code from net/http.

* Track ModifiedIndex, preventing missed updates
* Properly handle errors in presence protocol

Ensure that the Syncer listens on all interesting updates (added
compareAndSwap and compareAndDelete).