should set currentScreen_ at top of moveToPageEnded method

[KerryBatts]

When swiping, all's fine, but if I call moveToPage, this method isn't always passing the correct page number to the delegate.

I added a line to the top of the moveToPageEnded, and it solved this issue. I don't see any negative side effects, but let me know if I missed something.

add this to the top, before the comparison to prevScreen_:
currentScreen_ = [self pageNumberForPosition:self.position];