[BUGFIX beta] Add ducktyping of AdapterError

There are `instanceof` checks for `AdapterError` this removes them in
favor of checking for a property on the error, `isAdapterError` appears
on all errors that use `AdapterError` as the base.

addon/-private/adapters/errors.js

@@ -12,6 +12,7 @@ const PRIMARY_ATTRIBUTE_KEY = 'base';
   @namespace DS
 */
 export function AdapterError(errors, message = 'Adapter operation failed') {
+  this.isAdapterError = true;
   EmberError.call(this, message);
 
   this.errors = errors || [

addon/adapters/rest.js

@@ -853,7 +853,7 @@ export default Adapter.extend(BuildURLMixin, {
           requestData
         );
 
-        if (response instanceof AdapterError) {
+        if (response && response.isAdapterError) {
           Ember.run.join(null, reject, response);
         } else {
           Ember.run.join(null, resolve, response);

tests/unit/adapter-errors-test.js

@@ -10,24 +10,28 @@ test("DS.AdapterError", function(assert) {
   var error = new DS.AdapterError();
   assert.ok(error instanceof Error);
   assert.ok(error instanceof Ember.Error);
+  assert.ok(error.isAdapterError);
 });
 
 test("DS.InvalidError", function(assert) {
   var error = new DS.InvalidError();
   assert.ok(error instanceof Error);
   assert.ok(error instanceof DS.AdapterError);
+  assert.ok(error.isAdapterError);
 });
 
 test("DS.TimeoutError", function(assert) {
   var error = new DS.TimeoutError();
   assert.ok(error instanceof Error);
   assert.ok(error instanceof DS.AdapterError);
+  assert.ok(error.isAdapterError);
 });
 
 test("DS.AbortError", function(assert) {
   var error = new DS.AbortError();
   assert.ok(error instanceof Error);
   assert.ok(error instanceof DS.AdapterError);
+  assert.ok(error.isAdapterError);
 });
 
 var errorsHash = {