def get_extra_user_agents()
      @extra_user_agents_lock.synchronize do
        user_agents = @extra_user_agents.collect do |k, v|
          v.nil? ? k : '%s/%s' % [k, v]
        end
        @extra_user_agents.clear
        return user_agents
      end
    end
def get_extra_user_agents()
      @extra_user_agents_lock.synchronize do
        user_agents = @extra_user_agents.collect do |k, v|
          v.nil? ? k : '%s/%s' % [k, v]
        end
        @extra_user_agents.clear
        return user_agents
      end
    end
Generates an array of extra user agents to include in the user agent
 string.