Description:
------------
Calling stream_bucket_new on a write stream doesn't work (the same code fopening for reading works).

Reproduce code:
---------------
<?php /** Adapted from http://php.net/manual/function.stream-filter-register.php **/

/* Define our filter class */
class strtoupper_filter extends php_user_filter {
  function filter($in, $out, &$consumed, $closing)
  {
  	$new_bucket = stream_bucket_new($this->stream, "Uppercase text: ");
    if ($new_bucket === false) throw new Exception("stream_bucket_new should have returned a bucket");
    stream_bucket_append($out, $new_bucket);
    
    while ($bucket = stream_bucket_make_writeable($in)) {
      $bucket->data = strtoupper($bucket->data);
      $consumed += $bucket->datalen;
      stream_bucket_append($out, $bucket);
    }
    
	
    
    return PSFS_PASS_ON;
  }
}

/* Register our filter with PHP */
stream_filter_register("strtoupper", "strtoupper_filter")
    or die("Failed to register filter");

$fp = fopen("foo-bar.txt", "w");

/* Attach the registered filter to the stream just opened */
stream_filter_append($fp, "strtoupper");

fwrite($fp, "Line1\n");
fwrite($fp, "Word - 2\n");
fwrite($fp, "Easy As 123\n");

fclose($fp);

// Read the contents back out
 
readfile("foo-bar.txt");

?>


Actual result:
--------------
Warning: stream_bucket_new(): 5 is not a valid stream resource in bucket_new_testcase.php on line 7

Fatal error: Uncaught exception 'Exception' with message 'stream_bucket_new should have returned a bucket' 
Stack trace:
#0 [internal function]: strtoupper_filter->filter(Resource id #20, Resource id #21, 0, true)
#1 bucket_new_testcase.php(36): fclose(Resource id #5)
#2 {main}
  thrown in bucket_new_testcase.php on line 8