Log Message:
Update RMagick to 2.11.1.

Changes:
RMagick 2.11.1
    o Applied Alexey Borzenkov's mingw patches to extconf.rb.
    o Fixed a bug in Magick.trace_proc that could cause a segv at program exit
      with Ruby 1.9.1 (bug report by Larry Young)
    o Added new CompressionType enum values ZipSCompression, PixCompression,
      Pxr24Compression, B44Compression, B44ACompression (available in
      ImageMagick 6.5.5-4)