Prevent invalid UTF-8 byte sequences for Ruby 2.0 / 2.1 (1.9 untested)

to_utf8.rb

class String
  REPLACE_INVALID_WITH = '�'

  def to_utf8
    self.encode('utf-8', invalid: :replace, undef: :replace, replace: REPLACE_INVALID_WITH).
      chars.map{ |i| i.valid_encoding? ? i : REPLACE_INVALID_WITH }.join
  end
end