title: plupload to s3 with metadata
body: <p>I'm using Plupload to upload images to Amazon S3 and I want to include metadata in the upload.  </p>
  
  <p>The configurations I send to plupload look like this:  </p>
  
  <pre><code>$plupload_init = array(
                      'runtimes'            =&gt; 'html5,silverlight,flash,html4',
                      'browse_button'       =&gt; 'test_plupload-browse-button',
                      'container'           =&gt; 'testpluploadContainer',
                      'drop_element'        =&gt; 'test_drag-drop-area',
                      'file_data_name'      =&gt; 'file', 
                      'multiple_queues'     =&gt; false,
                      'max_file_size'       =&gt; '200mb',
                      'url'                 =&gt; 'http://myBucket.s3.amazonaws.com/',
                      'flash_swf_url'       =&gt; includes_url('js/plupload/plupload.flash.swf'),
                      'silverlight_xap_url' =&gt; includes_url('js/plupload/plupload.silverlight.xap'),
                      'filters'             =&gt; array(array('title' =&gt; __('Allowed Files'), 'extensions' =&gt; '*')),
                      'multipart'           =&gt; true,
                      'multipart_params'    =&gt; array(
                            // 'key' =&gt; '${filename}', // add folder later
                            'Filename' =&gt; '${filename}', 
                            'acl' =&gt; 'public-read',
                            'Content-Type' =&gt; '',
                            'success_action_status' =&gt; '201',
                            'AWSAccessKeyId' =&gt; $accessKeyId,
                            'policy' =&gt; $policy,
                            'signature' =&gt; $signature,
                      ),
                      'headers' =&gt; array(
                          'x-amz-meta-author' =&gt; 'test'
                      ),
                    );
  </code></pre>
  
  <p>This does upload the file, but does not have the metadata attached. I tried adding it to the array as its own element and to the multipart params but nothing worked.  </p>
  
  <p>Can someone please help me?</p>