Add maximum scrollbar size and fix minimum scrollbar size.

[Josh]

There is currently a minimum_bar_size property for scrollbars, but no matching maximum_bar_size property and minimum_bar size itself is bugged.

I have attached a patch which fixes both issues and does some micro-optimization and fixes some typos in the scrollbar code.

[Josh]

Thoroughly-tested patch in git format.

[historic_bruno]

When you create a ticket, please describe the bug in some detail so it can be confirmed and tested. I found discussion in the IRC logs ​today:

16:58 < Josh|> leper: You would get some really weird scaling issues
17:00 < Josh|> leper: You can see them by changing minimum_bar_size to something larger than the default in gui/common/setup.xml and you'll see the issue
17:01 < Josh|> (change it to something like 300 and open the learn to play window in-game and try scrolling)
17:01 < Josh|> I added maximum_bar_size because Pureon's new UI design will require that
17:03 < Josh|> The rest of the patch just fixes some /very/ inaccurate comments and correctly caches some calculations
17:04 < Josh|> (There were also some small changes to improve the code readability)
17:04 < leper> ok, I can reproduce the bug

[Josh]

V4, also don't render scrollbars unless there is something to scroll.

[Josh]

V5 (Style)

[peter]

In 13771:

General scrollbar improvements. Patch by Josh. Fixes #2080.

• Don't show the scrollbar when the contents aren't overflowing the visible area.
• Fix bugs in minimum bar sizing.
• Add capability to set a maximum bar size.
• Correct outdated/incorrect comments.

[alpha123]

Thanks for the patch. :)

[historic_bruno]

Josh, since you are somewhat familiar with the scrollbar logic now, what do you think about #877?