HorizontalPager changes

[shilgapira]

I've ran into some of the same issues other people have already described before here.

This pull request contains the changes I made to my copy of the file:

1. Added the fix posted by xsace to the problem with ListViews,
2. Added a testcase activity that demonstrates the problem (and how it goes away when the above fix is applied).
3. Added the code posted by Accused187 to persist the current page through orientation changes.
4. Fixed a couple of issues with the existing examples that prevented them from persisting the state properly.
5. Use a DecelerateInterpolator when animating the HorizontalPager so that long movements (e.g. when animating a transition between two pages that are not adjacent) look more natural.