Use query() for HasMany::purge()

[hexus]

This should do the trick. The only reason this isn't used is because it causes tests to fail, because InMemory storage does not set affected properly.

return (int) $this->storage()->query($this->target->table())
	->where($this->foreignKey, 0)
	->update(array(
		$this->foreignKey => $this->parent->get($this->localKey)
	))
	->cheers()->affected;

[hexus]

Woop woop.