Add test for lua_preload_file

test/lua_preload_file.lua

@@ -0,0 +1,7 @@
+--[[
+Load this test file by adding  
+  lua_preload_file ./lua_preload_file.lua
+to the civetweb.conf file
+]]
+
+mg.preload = "lua_preload_file successfully loaded"