Regression: using a column alias breaks ModelQueryResultWrapper for nested joined objects
Actually the behavior in master is now correct:

``` python
In [2]: generate_data()

In [3]: found = (Tweet.select(Tweet.message, User.username.alias('uname'))
   ...:              .join(User).where(Tweet.id == 1).get())

In [4]: found.user
Out[4]: <__main__.User at 0x7f35f01a54d0>

In [5]: found.user.uname
Out[5]: u'1'
```

So by using an alias, Peewee will assume you want the alias to be attribute on the object. Instead of `user.username` it is `user.uname` because of the alias.

PS thanks for the test code!

Repro:

``` python
import logging
import datetime

from peewee import *


logger = logging.getLogger(__name__)
database = SqliteDatabase(':memory:')


class User(Model):
    username = CharField(unique=True)
    class Meta:
        database = database


class Tweet(Model):
    user = ForeignKeyField(User, related_name='tweets')
    message = TextField()
    created_date = DateTimeField(default=datetime.datetime.now)
    is_published = BooleanField(default=True)

    class Meta:
        database = database


def generate_data():
    database.create_tables([User, Tweet])
    for username in ['1', '2', '3']:
        new_user = User.create(username=username)
        for msg in ['hi', 'hello', 'test']:
            Tweet.create(user=new_user, message=msg)    


def test_query():
    found = (Tweet.select(Tweet.message, User.username.alias('uname'))
             .join(User).where(Tweet.id == 1).get())
    logger.debug(found.user.username)


if __name__ == '__main__':
    generate_data()
    logging.basicConfig(level=logging.DEBUG)
    test_query()
```

output 2.6.1

```
DEBUG:peewee:('SELECT "t1"."message", "t2"."username" AS uname FROM "tweet" AS t1 INNER JOIN "user" AS t2 ON ("t1"."user_id" = "t2"."id") WHERE ("t1"."id" = ?) LIMIT 1', [1])
DEBUG:__main__:1
```

output master

```
DEBUG:peewee:('SELECT "t1"."message", "t2"."username" AS uname FROM "tweet" AS t1 INNER JOIN "user" AS t2 ON ("t1"."user_id" = "t2"."id") WHERE ("t1"."id" = ?) LIMIT 1', [1])
DEBUG:__main__:None
```
