API CHANGE: Added SapphireTest::$illegalExtensions and SapphireTest::$requiredExtensions for making tests depending on particular extension sets (from r89958)
git-svn-id: svn://svn.silverstripe.com/silverstripe/open/modules/sapphire/branches/2.4@96727 467b73ca-7a2a-4603-9d3b-597d59a354a9