Error when struct embeds exactly one reference

[sdboyer]

Embedding a single reference in a struct:

ref: {
  foo: string
} @cuetsy(kind="interface")

t: {
  ref
} @cuetsy(kind="interface")

Should result in...well, i'm not actually completely sure what this should result in, but this seems reasonable:

export interface ref {
  foo: string;
}

export interface t extends ref {}

However, the right outcome probably depends on the @cuetsy-specified kind.

Whatever the desirable output for each kind-case, none of them happen today. Instead, an error with the following super-helpful string is returned:

not a reference

This needs le fix.