Selecting multiple models / naive query
It appears peewee is not correctly assigning attributes from a related model:

``` python
from peewee import SqliteDatabase, Model, PrimaryKeyField, CharField, \
  IntegerField, ForeignKeyField
from playhouse.test_utils import test_database

test_db = SqliteDatabase(':memory:')

class Model1(Model):
  id = PrimaryKeyField()
  another_id = IntegerField()
  field = CharField()

  def __str__(self):
    return self.__class__.__name__ + '[' + ', '.join(["%s: %s" % (k, v) for k, v in self._data.items()]) + "]"

class Model2(Model):
  some_id = IntegerField() # PK
  another_id = IntegerField() # PK
  field2 = CharField()

  def __str__(self):
    return self.__class__.__name__ + '[' + ', '.join(["%s: %s" % (k, v) for k, v in self._data.items()]) + "]"

  class Meta():
    indexes = ((('some_id', 'another_id'), True),)

if __name__ == '__main__':

  with test_database(test_db, (Model1, Model2)):
    Model1.\
     create(id=1, another_id=1, field="example").\
     create(id=2, another_id=3, field="example")

    Model2.\
     create(some_id=1, another_id=1, field2="example2").\
     create(some_id=1, another_id=2, field2="example2").\
     create(some_id=2, another_id=3, field2="example2")

    res = (Model1
           .select(Model1, Model2)
           .join(Model2, on=(
               (Model1.id == Model2.some_id) &
               (Model1.another_id == Model2.another_id)
           ))
           .naive())
    print res.sql

    for a in res:
      print a
```
