Add method that resets last SELECT statement conditions

My use case:

```php
class Locale {
  private $loader;
  private $language;
  public function __construct( LocaleLoader $loader, $language ) {
    $this->loader = $loader;
    $this->language = $language;
  }
  public function get($term) {
    return $this->loader->get_translation($term, $this->language);
  }
}

interface LocaleLoader {
  public function get_translation($language);
}

class LocaleDBLoader implements LocaleLoader {
  private $model;
  public function __construct( ORM $model ) {
    $this->model = $model;
  }
  public function get_translation($term, $language = 'en') {
    return $this->model
                ->reset_conditions()
                ->where('term', $term)
                ->find_one()
                ->translations()
                ->where('langauge', $language)
                ->find_one();
  }
}


$loader = new LocaleDBLoader( Model::factory('Models\Term') );
$locale = new Locale( $loader, 'ca' );
echo 'In Catalan book is "' . $locale->get('book') . '" and pen is "' . $locale->get('pen') . '"';
```

Without `reset_conditions()` SELECT query adds conditions every time a method is called which results in wrong results.

Hopefully that makes sense.