message: give a meaningful error when the remote node does not handle /v2/prices
diff: @@ -49,6 +49,13 @@ export class BlockstackNetwork {
  getNamePrice(fullyQualifiedName: string) : Promise<*> {
  return fetch(`${this.blockstackAPIUrl}/v2/prices/names/${fullyQualifiedName}`)
  + .then((resp) => {
  + if (resp.status === 404) {
  + // old core node
  + throw new Error(`The upstream node does not handle the /v2/ price namespace`)
  + }
  + return resp
  + })
  .then(resp => resp.json())
  .then(resp => resp.name_price)
  .then(namePrice => {
  @@ -66,6 +73,13 @@ export class BlockstackNetwork {
  getNamespacePrice(namespaceID: string) : Promise<*> {
  return fetch(`${this.blockstackAPIUrl}/v2/prices/namespaces/${namespaceID}`)
  + .then((resp) => {
  + if (resp.status === 404) {
  + // old core node
  + throw new Error(`The upstream node does not handle the /v2/ price namespace`)
  + }
  + return resp
  + })
  .then(resp => resp.json())
  .then(namespacePrice => {
  if (!namespacePrice) {
  