title: BookshelfJS belongsToMany doesn't return duplicates
body: <p>I have two tables that are have the relationship <code>belongsToMany</code>. The pivot table also contains a column called <code>state</code> that could have 3 different values. Say my tables are <code>Table1</code> and <code>Table2</code>. </p>
  
  <p>There can be multiple entries for the same <code>Table1-Table2</code> relation with different <code>states</code>.</p>
  
  <p>I want to get all the pivot entries for <code>Table1</code> including any multiple entries for the same <code>Table2</code>. </p>
  
  <p>Unfortunately, the code</p>
  
  <pre><code>return this.belongsToMany(Table2, 'pivot_table1_table2').withPivot(['state'])
  </code></pre>
  
  <p>only returns the first entry for each <code>Table2</code>. </p>
  
  <p>Help is appreciated. </p>