fontdiff too sensitive to small changes?

[jamesgk]

I was hoping to add fonts from https://github.com/googlei18n/fontmake/issues/83#issue-156137760 to fontmake's end-to-end tests. However, I'm finding that fontdiff now reports differences for every line in the first example, even though the kerning issue should be fixed:

Here are the files I used: kerningTest.zip