Log Message:
Update RMagick to 2.9.2

Changes:
RMagick 2.9.2
    o Add new HorizontalTileEdgeVirtualPixelMethod,
      VerticalTileEdgeVirtualPixelMethod, CheckerTileVirtualPixelMethod
      VirtualPixelMethod enum values (available in ImageMagick 6.5.0-1)
    o Added BilinearForwardDistortion, BilinearReverseDistortion enums
      (available in ImageMagick 6.5.1-2)
    o Add missing composite operators to Magick::Draw#composite method
    o Add warning about dropping support for ImageMagick < 6.3.5 and
      Ruby < 1.8.5
    o Fix bug #25892, stack buffer overflow in Magick::TypeMetric.to_s
      (reported by Roman Simecek)