debug.traceback does not handle coroutines

[brandonbloom]

NOTE: Pull request is broken. Only providing the patch for discussion.

See https://www.lua.org/manual/5.1/manual.html#pdf-debug.traceback - The override of debug.traceback in terralib does not respect the thread parameter.

You get something like this:

$ terra

Terra -- A low-level counterpart to Lua

Stanford University
zdevito@stanford.edu

> = debug.traceback(coroutine.running(), 'on noez!', 2)
src/terralib.lua:433: attempt to perform arithmetic on local 'level' (a string value)
stack traceback:
    src/terralib.lua:433: in function <src/terralib.lua:431>

Compare to Lua:

~/Projects/plop $ lua
Lua 5.2.4  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> = debug.traceback(coroutine.running(), 'on noez!', 2)
on noez!
stack traceback:
    [C]: in ?
> ^D

I tried to fix the definition of debug.traceback in terralib, but the obvious solution produced 'error in error handling' for some non-obvious reason. I'll take another look at it soon if you don't have an idea offhand.