Fix virtual overloads

Fix virtual overloads

So I learned something today: the 'using' keyword can also be used to
import function names from the enclosing namespace. This not only
solves the spammy virtual overload warnings that the new-fangled protocol
stuff introduced unwittingly, but also removes the need to redefine
RemotePeer::handle<>() as a forward to Peer::handle<>().

Also, someone please kick the C++ inventors for making method lookup
not follow the Koenig rules (contrary to most other lookups...).