Use relative filepaths so differing envs play nice

If you're running your environment and your phpunit stack within vagrant, your base paths between your ide and what phpunit will generate will differ (ie, /path/to/my/code/my/project vs /vagrant). This commit alters the plugin to compare the tail end of the relative paths rather than do strict path comparison, which gives just enough leeway to cope with this scenario.

Would have used ends-with but thats not available in this implementation of xpath apparently.