title: Custom metabox for file upload return empty filename
body: <p>I want to attach a file to a post and "do something with it later". The file isn't being pulled over when I publish/update my post, the error I get is an empty filename. If I change the input type to text and submit I can get the text to save/display but trying to upload the file acts as though I haven't supplied the file to the form:</p>
  
  <p>form --</p>
  
  <p>function display_file_upload_meta_box($post_id,$post){</p>
  
  <pre><code>wp_nonce_field( basename( __FILE__ ), 'file_upload_meta_box_nonce' );
      ?&gt;
          &lt;p&gt;
              &lt;?php
                  $fileUpload= get_post_meta($object-&gt;ID,'file-upload-meta',true);
                  if(!$fileUpload)
                      $fileUpload = '';
                  echo 'file: '.$fileUpload;
              ?&gt;
              &lt;label for="file_upload_meta"&gt;Attach a file to this post&lt;/label&gt;
              &lt;input type="file" id="file_upload_meta" name="file_upload_meta" class="widefat"/&gt;
          &lt;/p&gt;
      &lt;?php
      }
  </code></pre>
  
  <p>code to upload file --</p>
  
  <pre><code>$new_meta_value = wp_upload_bits($_FILES["file_upload_meta"]['name'], null, file_get_contents($_FILES["file_upload_meta"]['tmp_name']));
  </code></pre>