We've historically had issues with very long, unbreakable lines. Prior

to 2.0, they would result in a horizontal scrollbar on the page,

requiring a lot of scrolling. In 2.0, they simply disappeared off the

edge of the parent container, with no ability to see the rest of the

contents.
In a best-case scenario, with long breakable lines, one column would end

up growing really wide while the other shrunk considerably (often

resulting in many rows taken for a single line, growing the page

length).
This change adds some sane management to the column widths. In

combination with the existing 'word-wrap: break-word;', we now set

minimum and maximum widths for the columns every time the page's width

changes. These widths are calculated based on the container's width,

factoring in the number of content columns and the widths taken by the

line numbers.
Each column gets a maximum of half and a minimum of 1/3 of the available

area. That maximum width, along with the word-wrap setting, allows long

non-breaking strings to wrap sanely, and also ensures that all wrapping

is constrained within a reasonable area to prevent the other column from

shrinking beyond readability.

Tested with normal diffs and ones with really long lines of random,

unbreakable characters.
I was able to resize the browser width to any width, and still get

readable, wrapped diffs on both sides, in both Chrome and Firefox.
Tested with modified files and added files, both with very long lines.
Tested with deleted files.
Generated an error with a diff and saw that the error box looked correct.