fixup! 9717ac1

Fixes the following under Ruby 1.9+

  1) ActsAsXapian::Search#words_to_highlight should handle non-ascii
  characters
    Failure/Error: s.words_to_highlight.should == ["adatigénylé", "word"]
      expected: ["adatigénylé", "word"]
      got: ["adatig\xC3\xA9nyl\xC3\xA9", "word"] (using ==)
    # ./spec/models/xapian_spec.rb:399:in
    # `block (2 levels) in <top (required)>'