Reordering fails with more than 31 book pages in a book

If somebody tries to reorder more than 31 pages in a book, he will face the fact that pages will not appear in the order s/he has put them in. The cause: the appropriate select has only 15 for #delta, which renders the reorder form useless if a book has more than 31 pages sharing the same depth. The solution: increase the #delta - 50 should be fairly enough, I think.