title: tagit : limiting tag creation to the given list by ajax
body: <p>i am using a jquery ui plugin for tagging : </p>
  
  <p><a href="https://github.com/aehlke/tag-it">https://github.com/aehlke/tag-it</a></p>
  
  <p>im having a few issues : </p>
  
  <ol>
  <li><p>when a user selects from the list, i want to save the id and the value for that tag. </p></li>
  <li><p>only create tags from the list brought back by the AJAX call</p>
  
  <pre><code>$(function() {
    $('#tags').tagit({tagSource:function( request, response ) {
  $.ajax({
  type:"GET",
  url: "http://some_link",
  dataType: "jsonp",
  data:{
      term:request.term,
      }, 
      success: function( data ) {
          response( $.map( data, function( item ) {
              return {
                  label: item.label,
                  value: item.value,
                  id:item.id
              };  
          }));
      }   
      });
  }
  , triggerKeys: ['enter', 'comma', 'tab']});
  });
  </code></pre></li>
  </ol>