CIST_TAIL
ar->istailcall = (ci) ? ci->callstatus & CIST_TAIL : 0;
if (ci && !(ci->callstatus & CIST_TAIL) && isLua(ci->previous))
ci->callstatus |= CIST_TAIL;
oci->callstatus |= CIST_TAIL; /* function was tail called */