0.9.x - 1.0.x regression - AttributeError: entity when accessing query.column_descriptions when using label() with attribute of aliased entity

After upgrading to 1.0.2 resp. 1.0.3 SQLAlchemy, this error popped up. It happens when label() is used with attribute of aliased entity.

#!/usr/bin/python
# -*- coding: utf-8 -*-
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import aliased

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    username = Column(String(255))
    realname = Column(String(255))

e = create_engine("postgresql://user:passwd@localhost/db_name", echo=True)
Base.metadata.create_all(e)

session = Session(e)

user = aliased(User,name="user")

q = session.query(user.username.label("username"))

print(q.column_descriptions)

Traceback (most recent call last):
  File "/home/pavel/python/hores/src/sqlalchemytest.py", line 27, in <module>
    print(q.column_descriptions)
  File "/usr/lib64/python3.4/site-packages/sqlalchemy/orm/query.py", line 2583, in column_descriptions
    for ent in self._entities
  File "/usr/lib64/python3.4/site-packages/sqlalchemy/orm/query.py", line 2583, in <listcomp>
    for ent in self._entities
  File "/usr/lib64/python3.4/site-packages/sqlalchemy/orm/util.py", line 398, in __getattr__
    raise AttributeError(key)
AttributeError: entity

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