SciTools/cartopy — pull request #451 by rhattersley (2014-06-27 10:54:18+00:00)
Title: Allow for very minor source/rendering differences.

An example diff image that the new tolerance just about lets pass:

![result-web_tiles-failed-diff](https://cloud.githubusercontent.com/assets/917914/3410588/4b4ec8e4-fde9-11e3-94c0-12f93b7f1360.png)