Fixes `join` with related models which have "associative" conditions.

Filtering for relations configured this way (associative conditions) was NOT working:
```php
var $hasOne = array('Located' => array('conditions' => array(
    'Located.model' => 'Employee',
)));
```

Filtering for relations configured this way was working:
```php
var $hasOne = array('Located' => array('conditions' => array(
    'Located.model = "Employee"',
)));
```