PasswordField does not seem to work with Postgres
Thanks :)
 Same code, with updated peewee:

```
Traceback (most recent call last):
  File "peewee_password_field.py", line 19, in <module>
    assert user.password.check_password('password')
  File "/home/ybon/.virtualenvs/p3/local/lib/python3.4/site-packages/playhouse/fields.py", line 47, in check_password
    return hashpw(password, self) == self
  File "/home/ybon/.virtualenvs/p3/local/lib/python3.4/site-packages/bcrypt/__init__.py", line 66, in hashpw
    raise ValueError("Invalid salt")
ValueError: Invalid salt
```

Missing unittests in Postgres? :)
 (I can't reopen the issue, dunno why…)
 I'm not sure what's going on exactly. Having trouble getting `bcrypt` to build in a python3 virtualenv but testing locally with python2+sqlite is working fine. What is the salt of the particular password you're having trouble with, and what is it's type?
 Thanks for looking into this @coleifer :)

I'm just running the snippet from https://github.com/coleifer/peewee/issues/766#issue-118223951 (I'm on IRC if it helps debugging).
 This diff fixes my usecase:

``` diff
diff --git a/playhouse/fields.py b/playhouse/fields.py
index fcebae7..bfa2d90 100644
--- a/playhouse/fields.py
+++ b/playhouse/fields.py
@@ -47,7 +47,7 @@ if hashpw and gensalt:
             return hashpw(password, self) == self


-    class PasswordField(TextField):
+    class PasswordField(BlobField):
         def __init__(self, iterations=12, *args, **kwargs):
             if None in (hashpw, gensalt):
                 raise ValueError('Missing library required for PasswordField: bcrypt')
```

Basically, the issue seems to be that we are sending bytes to a Text field in Postgres.
Not sure though why tests passe without this change (they also pass with the fix)…
 Ah, now I know why tests passe even without the fix: they are never ran with postgres…
Even if I pass `--engine postgres`, simply because the Model used in the tests only use "in memory database": https://github.com/coleifer/peewee/blob/master/playhouse/tests/test_extra_fields.py#L22

Is there a reason for that?

``` python
import peewee
from playhouse.fields import PasswordField

db = peewee.PostgresqlDatabase('peewee')


class User(peewee.Model):
    username = peewee.CharField(max_length=10)
    password = PasswordField()

    class Meta:
        database = db


if __name__ == '__main__':
    User.create_table()
    user = User.create(username='yo', password='password')
    user = User.get(User.id == user.id)
    assert user.password.check_password('password')
```

Fails with this traceback:

```
Traceback (most recent call last):
  File "peewee_password_field.py", line 22, in <module>
    user = User.get(User.id == user.id)
  File "/home/ybon/.virtualenvs/ban/lib/python3.4/site-packages/peewee.py", line 4393, in get
    return sq.get()
  File "/home/ybon/.virtualenvs/ban/lib/python3.4/site-packages/peewee.py", line 2812, in get
    return clone.execute().next()
  File "/home/ybon/.virtualenvs/ban/lib/python3.4/site-packages/peewee.py", line 2029, in next
    obj = self.iterate()
  File "/home/ybon/.virtualenvs/ban/lib/python3.4/site-packages/peewee.py", line 2015, in iterate
    return self.process_row(row)
  File "/home/ybon/.virtualenvs/ban/lib/python3.4/site-packages/peewee.py", line 2090, in process_row
    setattr(instance, column, func(row[i]))
  File "/home/ybon/.virtualenvs/ban/lib/python3.4/site-packages/playhouse/fields.py", line 66, in python_value
    return PasswordHash(value)
TypeError: string argument without an encoding

```
