title: typeahead.js deduplicate between prefetch and remote datasources
body: <p>I'm using typeahead.js with both prefetch and remote
  <a href="http://twitter.github.io/typeahead.js/examples/#custom-templates" rel="nofollow">http://twitter.github.io/typeahead.js/examples/#custom-templates</a></p>
  
  <pre><code>$(document).ready(function() {
  var castDirectors = new Bloodhound({
    datumTokenizer: Bloodhound.tokenizers.obj.whitespace('value'),
    queryTokenizer: Bloodhound.tokenizers.whitespace,
    prefetch: '../api/v1/search/people_typeahead',
    remote: '../api/v1/search/people_typeahead?q=%QUERY'
  });
  
  castDirectors.initialize();
  
  $('#remote .typeahead').typeahead(null, {
    name: 'cast-directors',
    displayKey: 'value',
    source: castDirectors.ttAdapter(),
      templates: {
          empty: [
        '&lt;div class="empty-message"&gt;',
        'no matching names',
        '&lt;/div&gt;'
      ].join('\n'),
          suggestion: Handlebars.compile('&lt;p&gt;&lt;a href="{{link}}"&gt;{{value}}&lt;/a&gt;&lt;/p&gt;')
      }       
  });
  });
  </code></pre>
  
  <p>However, there are duplicated entries in the prefetch JSON and remote JSON. How can I dedup so that it only shows one entry?</p>