prepare_backtrace

# File lib/drb/drb.rb, line 1119
    def self.prepare_backtrace(uri, result)
      prefix = "(#{uri}) "
      bt = []
      result.backtrace.each do |x|
        break if /`__send__'$/ =~ x 
        if /^\(druby:\/\// =~ x
          bt.push(x)
        else
          bt.push(prefix + x)
        end
      end
      bt
    end