implements() with multiple RemoteInterfaces

[Brian Warner]

it would be awfully useful if Referenceable subclasses could indicate that they implement multiple RemoteInterfaces?, not just one. This only-one-RemoteInterface? limitation requires users to play weird games and mix together interfaces that really ought to be separate.

To fix this, we'll need to change the way that Referenceables get sent over the wire the very first time. At the moment, there's a slot in the serialized (my-reference) sequence for a RemoteInterface? name: that needs to accept either a single string or a list of strings.