Share proto object among multiple lua vm

[云风 <cloudwu@...>]

There are many lua vm (more then 10K) in one process in our system. We
run all of them by a thread pool. It runs well except huge memory
usage , because the same byte codes exist in each vm .

So I make a patch to lua 5.2.3 to share the same Proto objects among
multiple lua vm [1].

It introduces a new api : void lua_clonefunction (lua_State *L, const void * fp)

We can get a lua function's pointer by lua_topointer first, and then
pass it to lua_clonefunction to generate a new lua closure. The origin
lua function can be in different  lua vm .

So we can put all the functions need to be share in an independent lua
vm , and share them to other lua vm in the same process.

It can also accelerate the vm's bootstrap , because no parser or
undump needed [2].

[1] https://gist.github.com/cloudwu/9656839
[2] https://gist.github.com/cloudwu/9656890

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