优化http出错抛出更详细的错误信息 (#1900)

* 优化http出错抛出更详细的错误信息

* 优化http err_info写法

lualib/http/httpd.lua

@@ -2,6 +2,11 @@ local internal = require "http.internal"
 
 local string = string
 local type = type
+local assert = assert
+local tonumber = tonumber
+local pcall = pcall
+local ipairs = ipairs
+local pairs = pairs
 
 local httpd = {}