tweak_backtrace

# File lib/spec/runner/backtrace_tweaker.rb, line 43
      def tweak_backtrace(error)
        return if error.backtrace.nil?
        tweaked = error.backtrace.collect do |message|
          clean_up_double_slashes(message)
          kept_lines = message.split("\n").select do |line|
            IGNORE_PATTERNS.each do |ignore|
              break if line =~ ignore
            end
          end
          kept_lines.empty?? nil : kept_lines.join("\n")
        end
        error.set_backtrace(tweaked.select {|line| line})
      end