skynet.init rework, See #1322 (#1323)

* skynet.init rework, See #1322

* restore init_list #1322

* xpcall init_all, See #1322

lualib/loader.lua

@@ -45,4 +45,6 @@ if LUA_PRELOAD then
 	LUA_PRELOAD = nil
 end
 
+_G.require = (require "skynet.require").require
+
 main(select(2, table.unpack(args)))