default handle-message method prints args
remember-object picks an id if none supplied
get-global is counterpart to register-global
pack-arg: assert that the argument for a new id is reasonable
length word in string arg includes terminating \0
a new_id with no interface is special-cased in scanner.c to become three arguments on the wire.  bodge a fix here to match it
registry-bind /seems/ to work, except that reply messages are unparseable