Log Message:
Update graphics/ruby-cairo to 1.6.0.  Changes from version 1.5.1 include:

   * Support cairo 1.6.0.
   * Improve Quartz surface support. (thanks to kimura wataru, OBATA Akio)
   * Support Cairo::Win32PrintingSurface.
   * Support Cairo::QuartzImageSurface.
   * Support ruby 1.9.1.
   * Add Cairo::Paper.
     * Improve size specification of Cairo::PSSurface,
       Cairo::PDFSurface, Cairo::SVGSurface.