Even number of pages - first and last page

[mbelic]

Thanks for great library. One question: When flipping the second to last page (closing the book) it is still visible under it until the flip animation is over, then it disappears. The shadow is still present. Similarly if you flip from page 2 to page one (closing the book from front), page 2 is visible under page 2 while it is animating and then the same thing happens. I thought about introducing 2 additional white pages in the front and at the back to avoid this, but is there any other way to fix this issue?