gitk: bug viewing diffs with the word items

Hi.

I see a bug with the diff view of gitk.

when the text " <items>" or " </items>" appears

on one of the surrounding contexts lines in a diff,

gitk treats it as part of the "Old Version", highlighting it in red,

and hiding it if "New Version" is selected

I don't know if any other magic words are affected

ied it with the master

bug confirmed exists in github/git/git/master

I created a small repository that shows the error for me:

clone it to reproduce the behavior

https://github.com/d4ddi0/gitk_diff_view

~Joshua Clayton