Known test failures

Since tests for Drupal 7 keep breaking unexpectedly, I started doing <a href="http://groups.drupal.org/node/11993">test snapshots</a> every few days to track progress. After the first two runs there's good and bad news - less tests fail each time, but they're often different ones. Getting to a 100% pass rate is a pre-requisite for encouraging more people to write tests and extending the Drupal 7 release cycle, so hopefully we'll get the remaining ones fixed up pretty soon.