Previously, the current line was only moved as much as necessary so that it's in
view again. This had the problem that when jumping downwards from hunk to hunk
with the right-arrow key, only the first line of the new hunk was shown at the
bottom of the window. I prefer to put the selected line in the middle of the
view in this case, so that I can see more of the newly selected hunk.
This has the consequence that when scrolling through the view line by line using
down-arrow, the view jumps by half a screen whenever I reach the bottom. I can
see how some users might be opposed to this change, but I happen to like it too,
because it allows me to see more context of what's ahead.
