Tracebacks in coroutines

[RLake@...]

It was good to hear that this will be
addressed in the next version.

In the meantime, the following appears
to work; no warranties, do not use under the influence of heavy machinery,
etc.

In ldebug.c, replace the definition
of luaG_errormsg with the following:

 void luaG_errormsg (lua_State
*L) {
   const TObject *errfunc;
   if (L->errfunc != 0)
{  /* is there an error handling function? */
     errfunc = restorestack(L,
L->errfunc);
  } else {
    errfunc = luaH_getstr(hvalue(gt(L)),
luaS_new(L, "_TRACEBACK"));
  }
  if (ttisfunction(errfunc)) {
    setobjs2s(L->top, L->top
- 1);  /* move argument */
    setobj2s(L->top - 1,
errfunc);  /* push function */
    incr_top(L);
    luaD_call(L, L->top
- 2, 1);  /* call it */
  }
  luaD_throw(L, LUA_ERRRUN);
}

Of course, all this does is generate
a traceback; it is still necessary to check the return from coroutine.resume/lua_resume.