code: func gaePrepContent(in io.Reader) io.Reader {
  	var prefix = []byte("#appengine:")
  	out, w := io.Pipe()
  	go func() {
  		r := bufio.NewReader(in)
  		drop := false
  		for {
  			b, err := r.ReadBytes('\n')
  			if err != nil && err != io.EOF {
  				w.CloseWithError(err)
  				return
  			}
  			if bytes.HasPrefix(b, prefix) {
  				b = b[len(prefix):]
  				if b[0] == ' ' {
  					// Consume a single space after the prefix.
  					b = b[1:]
  				}
  				drop = true
  			} else if drop {
  				if len(b) > 1 {
  					b = nil
  				}
  				drop = false
  			}
  			if len(b) > 0 {
  				w.Write(b)
  			}
  			if err == io.EOF {
  				w.Close()
  				return
  			}
  		}
  	}()
  	return out
  }
docs: // gaePrepContent returns a Reader that produces the content from the given
  // Reader, but strips the prefix "#appengine:", optionally followed by a space, from each line.
  // It also drops any non-blank line that follows a series of 1 or more lines with the prefix.