改写INTERVAL-SEARCH的代码，使得当所有区间都是开区间时，它也能正确地工作。
INTERVAL-SEARCH(T,i)
{
IBST_NODE x = T->left;
while (x != T&&Interval_overlap(i, &x->data) == 0) {
if (x->left != T&&x->left->max >= i->start)
{
x = x->left;
}
else
x = x->right;
}
return x; 
