luaL_checkstack
luaL_checkstack(L, nup, "too many upvalues");
LUALIB_API void (luaL_checkstack) (lua_State *L, int sz, const char *msg);
luaL_checkstack(L, n, "string slice too long");
luaL_checkstack(ms->L, nlevels, "too many captures");
luaL_checkstack(L, 40, ""); /* assume array is smaller than 2^40 */