title: jquery Bootstrap tooltip title callback function not executing
body: <p>When creating tooltips the following code should be used to change the shown content of the tooltip to whatever is returned by the function in the title option:</p>
  
  <pre><code>$('.tooltip').tooltip({
              html: true,
              title: function(el){return 'custom content';}
          });
  </code></pre>
  
  <p>The tooltip's are not shown at all or return the title attribute contents, but the callback function is not executed at all. No warnings/errors are shown in the console.</p>