* rulesets/Entity.h, rulesets/Entity.cpp: Set argument names on
some methods. Add a new method allowing a property to be set
externally.
* server/ExternalProperty.cpp, server/ExternalProperty.h: Add a new
property which reflects whether an entity is connected to the
outside world via an external mind.
* server/Connection.cpp, server/Connection.h: Add a new method which
hooks up an avatar to the connection, installing an ExternalProperty
if necessary.
* server/Account.cpp: Use the new Connection method to hook up
existing avatars.
