keystone s3_token middleware not usable

s3 middleware authentication is causing swift-proxy server to fail to start:

proxy-server (21880) appears to have stopped
Starting proxy-server...(/etc/swift/proxy-server.conf)
Traceback (most recent call last):
  File "/usr/bin/swift-proxy-server", line 22, in <module>
    run_wsgi(conf_file, 'proxy-server', default_port=8080, **options)
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 256, in run_wsgi
    loadapp(conf_path, global_conf={'log_name': log_name})
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 107, in wrapper
    return f(conf_uri, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 247, in loadapp
    return loadobj(APP, uri, name=name, **kw)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 271, in loadobj
    global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 296, in loadcontext
    global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 320, in _loadconfig
    return loader.get_context(object_type, name, global_conf)
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 55, in get_context
    object_type, name=name, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 450, in get_context
    global_additions=global_additions)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 562, in _pipeline_app_context
    for name in pipeline[:-1]]
  File "/usr/lib/python2.7/dist-packages/swift/common/wsgi.py", line 55, in get_context
    object_type, name=name, global_conf=global_conf)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 458, in get_context
    section)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 517, in _context_from_explicit
    value = import_string(found_expr)
  File "/usr/lib/python2.7/dist-packages/paste/deploy/loadwsgi.py", line 22, in import_string
    return pkg_resources.EntryPoint.parse("x=" + s).load(False)
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 2015, in load
    entry = __import__(self.module_name, globals(),globals(), ['__name__'])
  File "/usr/lib/python2.7/dist-packages/keystone/middleware/__init__.py", line 18, in <module>
    from keystone.middleware.core import *
  File "/usr/lib/python2.7/dist-packages/keystone/middleware/core.py", line 21, in <module>
    from keystone.common import utils
  File "/usr/lib/python2.7/dist-packages/keystone/common/utils.py", line 32, in <module>
    from keystone import exception
  File "/usr/lib/python2.7/dist-packages/keystone/exception.py", line 63, in <module>
    class ValidationError(Error):
  File "/usr/lib/python2.7/dist-packages/keystone/exception.py", line 64, in ValidationError
    message_format = _("Expecting to find %(attribute)s in %(target)s."
NameError: name '_' is not defined

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: swift-proxy 1.9.1-0ubuntu2
ProcVersionSignature: Ubuntu 3.11.0-4.9-generic 3.11.0-rc7
Uname: Linux 3.11.0-4-generic x86_64
ApportVersion: 2.12.4-0ubuntu1
Architecture: amd64
Date: Thu Sep 26 09:14:50 2013
Ec2AMI: ami-00000092
Ec2AMIManifest: FIXME
Ec2AvailabilityZone: nova
Ec2InstanceType: m1.small
Ec2Kernel: aki-00000002
Ec2Ramdisk: ari-00000002
MarkForUpload: True
PackageArchitecture: all
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: swift
UpgradeStatus: No upgrade log present (probably fresh install)