Re: OP_HALT is really useful

I've just spent some time playing with VS Code, which has a couple very nice community written Lua debuggers.  However, as Seungjae Lee notes in his README.md, the performance hit that one sees from using one of these debuggers is reduced dramatically if one registers breakpoints using Dan Tull's OP_HALT patch in place of debug.sethook().

I don't fully understand the reasons /why/ OP_HALT is so useful, but, I can confirm that, in my own use case at least, implementing OP_HALT changes the overhead from running with a debugger from 'severe' to 'unnoticeable'.

Unfortunately, Dan's original patch is now 7+ years old, and Seungjae Lee's 5.1.5 version is written against a version of the codebase that's only slightly newer.  I have managed to apply Seungjae Lee's version of OP_HALT to my own modded copy of Lua 5.2, and it appears to work well. 

So, if there's a need for a 5.2 version, interested parties should let me know, and perhaps we can create an official-ish entry for OP_HALT on the power patches page.  (This is not an entirely altruistic suggestion -- I suspect there may be some some quirks with the interaction of OP_HALT and 5.2-era features like GOTOs that could use a bit more investigation.)

Beyond that, I would submit to Roberto et al. that adding something OP_HALT-ish to the official Lua sources might not be a bad idea -- I was shocked by what a difference it makes.

-Sven