Continuation of issue 167628.
As a result of the fix for issue 168075, the visual discrepancies now only become noticeable in larger files, and 
Ctrl+Down now behaves as expected.

Issues that remain:

1) In a 500-line file with an error on line 470, with a 50-line editor viewport, after scrolling down as much as 
possible, line 470 is visible in the viewport, while the corresponding error marker beside the scrollbar is above the 
slider, suggesting an error outside of the visible area.

2) Ctrl+End scrolling behavior is inconsistent: Depending on the distance of the caret position from the last line 
(and/or the scroll position?), Ctrl+End causes all, some, or none of the extra space to become visible. In particular, 
when the last line of the document is already visible, then Ctrl+End does not cause any scrolling further down. Similar 
for PageDown, and Cursor-Down on the last line, though for them it's debatable what the expected behavior would be.

To fix (1), the only solution I'm aware of is the one I suggested in issue 167628.

As for (2): One possible guideline could be to make these actions behave as if the file actually had more lines (an 
amount corresponding to the extra space), and cause scrolling accordingly, but of course still restrict the caret to 
the actual file content.

In particular for point (1), I could see the following compromise: Restrict the extra space further, to a constant 
number N of lines (or possibly to max(N, viewport.height/3)). I actually don't see how more than 3-5 lines would be 
really helpful. Make N configurable so users can set it to their preference (possibly to 0).

An additional suggestion would be to cause scrolling when the caret comes closer to the viewport than those same N 
lines. For example when moving down with the caret line by line, the editor would scroll not when the caret reaches the 
bottom of the viewport, but already N lines before that. This is a common feature in editors, and would be perfectly in 
line with having a corresponding extra space at the bottom. See Vim's "scrolloff" option for example: 
http://vimdoc.sourceforge.net/htmldoc/options.html#'scrolloff'