Carousel page block arrows sit outside dimensions

[allanaaa]

For the most part users will put a carousel block at the full page width, but if it's floated in normal flow, or getting a limited width in grid flow, the arrows will sit outside its required dimensions and possibly overflow into another container.

(It's the only thing I've seen so far in the new grid layout that is overflowing its width like this, so I would release this with S 4.1.)

[kimisgold]

This happens in normal flow context as well but might not be as noticeable. I've pushed a fix that keeps the arrows within the width of the content container.