/**
  * Deletes a comment applied to a specific image in Picasa Web Albums.
  *
  * @access public
  * @param string $username           The username on the account that the comment is in.
  * @param string $albumid            The id number of the album that the comment to delete is in.
  * @param string $imageid            The id number of the image that the comment is on.
  * @param string $tag                The id number of the comment to delete.
  * @return boolean                   true if the comment was successfully deleted.
  * @throws {@link Picasa_Exception}  If something was wrong with the post to Picasa.  A specific subclass of
  *                                   {@link Picasa_Exception} will be thrown based on what kind of problem was
  *                                   encountered, unless the type of error was unknown, in which case {@link Picasa_Exception}
  *                                   itself will be thrown.  In the case of an exception, the album is not deleted.
  */
 public function deleteComment($username, $albumid, $imageid, $commentid)
 {
     $host = Picasa::$PICASA_URL;
     $path = '/data/entry/api/user/' . $username . '/albumid/' . $albumid . '/photoid/' . $imageid . '/commentid/' . $commentid;
     $specialHeaders = array(1 => $this->getAuthHeader());
     try {
         Picasa::do_request($host, $path, null, "DELETE", $specialHeaders);
         return true;
     } catch (Picasa_Exception $e) {
         throw Picasa::getExceptionFromInvalidPost($e->getResponse(), $e->getMessage());
     }
 }