message: check structure equality for StructureElement.Loci
diff: @@ -50,6 +50,7 @@ export namespace Loci {
  }
  export function areEqual(a: Loci, b: Loci) {
  + if (a.structure !== b.structure) return false
  if (a.elements.length !== b.elements.length) return false
  for (let i = 0, il = a.elements.length; i < il; ++i) {
  const elementA = a.elements[i]
  