Coroutines do not unwind the stack in case of errors

Back to how it was, a coroutine does not unwind its stack in case of
errors (and therefore do not close its to-be-closed variables). This
allows the stack to be examined after the error. The program can
use 'coroutine.kill' to close the variables.

The function created by 'coroutine.wrap', however, closes the
coroutine's variables in case of errors, as it is impossible to examine
the stack any way.

ldo.c

@@ -686,10 +686,8 @@ LUA_API int lua_resume (lua_State *L, lua_State *from, int nargs,
   if (likely(!errorstatus(status)))
     lua_assert(status == L->status);  /* normal end or yield */
   else {  /* unrecoverable error */
-    status = luaF_close(L, L->stack, status);  /* close all upvalues */
     L->status = cast_byte(status);  /* mark thread as 'dead' */
-    luaD_seterrorobj(L, status, L->stack + 1);  /* push error message */
-    L->ci = &L->base_ci;  /* back to the original C level */
+    luaD_seterrorobj(L, status, L->top);  /* push error message */
     L->ci->top = L->top;
   }
   *nresults = (status == LUA_YIELD) ? L->ci->u2.nyield