Using select in constructor/arg ignores that arg in duplicate checks

It's similar to [Issue 392](https://code.google.com/p/mybatis/issues/detail?id=392).
If you have resultMap like:
```xml
<resultMap id="postLiteMap2NestedWithSelect" type="domain.blog.BlogLite">
  <id column="blog_id" property="id" />
  <collection property="posts" ofType="domain.blog.PostLite">
    <constructor>
      <arg javaType="domain.blog.PostLiteId" column="{id=id}" select="selectPostLiteId" />
      <arg javaType="_int" column="blog_id"/>
    </constructor>
  </collection>
</resultMap>
```

then the `arg` with `select` is ignored and posts are unique based on `blog_id` (which, in this case, is the same). Hence all posts but one are ignored.