Last known good build: http://buildbot.mongodb.org/builders/OS%20X%2010.5%2064-bit%20Weekly%20Slow%20Tests/builds/71

First failing buildbot build: http://buildbot.mongodb.org/builders/OS%20X%2010.5%2064-bit%20Weekly%20Slow%20Tests/builds/72

Almost all failures since build 72 appear to be similar. MCI builds show the same outcome (e.g. all OS X build variants fail the slowWeekly tests): http://mci.10gen.com/ui/task_history/slow_weekly_tests?osx-108=on&osx-108-cxx11-debug=on&osx-108-debug=on&osx-108-dur-off=on