Fix crash w/ polymorphic errors in JSONSerializer

Use a specialized version of normalizeRelationships for errors rather
than relying on the regular one that expects a `type` property.

packages/ember-data/lib/serializers/json-serializer.js

@@ -2,7 +2,9 @@ import Serializer from "ember-data/system/serializer";
 
 var get = Ember.get;
 var isNone = Ember.isNone;
+var isArray = Ember.isArray;
 var map = Ember.ArrayPolyfills.map;
+var forEach = Ember.ArrayPolyfills.forEach;
 var merge = Ember.merge;
 
 /**
@@ -274,10 +276,41 @@ export default Serializer.extend({
   normalizeErrors: function(typeClass, hash) {
     this.normalizeId(hash);
     this.normalizeAttributes(typeClass, hash);
-    this.normalizeRelationships(typeClass, hash);
+    this.normalizeRelationshipErrors(typeClass, hash);
     this.normalizeUsingDeclaredMapping(typeClass, hash);
   },
 
+  /**
+    @method normalizeRelationshipErrors
+    @private
+  */
+  normalizeRelationshipErrors: function(typeClass, hash) {
+    if (!this.keyForRelationship) {
+      return;
+    }
+
+    typeClass.eachRelationship(function(key, relationship) {
+      var payloadKey = this.keyForRelationship(key, relationship.kind);
+      if (key !== payloadKey && hash.hasOwnProperty(payloadKey)) {
+        hash[key] = hash[payloadKey];
+        delete hash[payloadKey];
+      }
+
+      if (!hash || !hash[key]) {
+        return;
+      }
+      if (relationship.kind === 'hasMany' && isArray(hash[key])) {
+        forEach.call(hash[key], function(errors) {
+          if (errors) {
+            this.normalizeErrors(relationship.type, errors);
+          }
+        }, this);
+      } else {
+        this.normalizeErrors(relationship.type, hash[key]);
+      }
+    }, this);
+  },
+
   /**
     Looks up the property key that was set by the custom `attr` mapping
     passed to the serializer.