inViewport returns true for element starting at window.innerHeight

Maybe it's just a matter of definition, but an element starting exactly at the invisible first pixel under viewport is considered "inViewport". Why?

http://plnkr.co/edit/rurMeic3TAIEXQ8OHJLz?p=preview

Considering that position counting starts at 0, an element having `top=viewportH()` isn't really in the viewport IMO.
