Feed error messages through a cors wrapper so that people on other domains can see what's happening.

endpoints/api/tag.py

@@ -1,7 +1,5 @@
-from flask.ext.restful import abort
-
 from endpoints.api import (resource, nickname, require_repo_read, require_repo_admin,
-                           RepositoryParamResource, log_action)
+                           RepositoryParamResource, log_action, NotFound)
 from endpoints.api.image import image_view
 from data import model
 from auth.auth_context import get_authenticated_user
@@ -36,7 +34,7 @@ class RepositoryTagImages(RepositoryParamResource):
     try:
       tag_image = model.get_tag_image(namespace, repository, tag)
     except model.DataModelException:
-      abort(404)
+      raise NotFound()
 
     parent_images = model.get_parent_images(tag_image)