Lots of tracebacks for authenticated calls

We're getting around 4k of these tracebacks on a daily basis:

Traceback (most recent call last):
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/core/handlers/base.py", line 111, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/views/decorators/vary.py", line 22, in inner_func
    response = func(*args, **kwargs)
  File "/usr/lib/python2.6/dist-packages/piston/resource.py", line 74, in __call__
    if not self.authentication.is_authenticated(request):
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/src/webcatalog/auth.py", line 81, in is_authenticated
    consumer, token, parameters = self.validate_token(request)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/src/webcatalog/auth.py", line 140, in validate_token
    return oauth_server.verify_request(oauth_request)
  File "/usr/lib/python2.6/dist-packages/oauth/oauth.py", line 436, in verify_request
    self._check_signature(oauth_request, consumer, token)
  File "/usr/lib/python2.6/dist-packages/oauth/oauth.py", line 500, in _check_signature
    self._check_nonce(consumer, token, nonce)
  File "/usr/lib/python2.6/dist-packages/oauth/oauth.py", line 528, in _check_nonce
    nonce = self.data_store.lookup_nonce(consumer, token, nonce)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/src/webcatalog/models/oauthtoken.py", line 204, in lookup_nonce
    Nonce.create(consumer.key, token.key, nonce)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/src/webcatalog/models/oauthtoken.py", line 149, in create
    return consumer.nonce_set.create(token=token, nonce=nonce)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/fields/related.py", line 436, in create
    return super(RelatedManager, self.db_manager(db)).create(**kwargs)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/manager.py", line 138, in create
    return self.get_query_set().create(**kwargs)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/query.py", line 360, in create
    obj.save(force_insert=True, using=self.db)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/base.py", line 460, in save
    self.save_base(using=using, force_insert=force_insert, force_update=force_update)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/base.py", line 553, in save_base
    result = manager._insert(values, return_id=update_pk, using=using)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/manager.py", line 195, in _insert
    return insert_query(self.model, values, **kwargs)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/query.py", line 1436, in insert_query
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/sql/compiler.py", line 791, in execute_sql
    cursor = super(SQLInsertCompiler, self).execute_sql(None)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/models/sql/compiler.py", line 735, in execute_sql
    cursor.execute(sql, params)
  File "/srv/uwc.ubuntu.com/production/ubuntu-webcatalog/sourcecode/django/django/db/backends/postgresql_psycopg2/base.py", line 44, in execute
    return self.cursor.execute(query, args)
IntegrityError: duplicate key value violates unique constraint "webcatalog_nonce_nonce_key"

This might be that we need to clear out the nonce table on a daily basis.