BUGFIX Enforcing creation of temp database in SapphireTest->setUp() t…

…o avoid writing to production databases. This check should only kick in for single test case runs, as the temp database connection should be set in a dev/tests/all run after the first db-related test anyway. (see #5034) (from r99342)

git-svn-id: svn://svn.silverstripe.com/silverstripe/open/modules/sapphire/trunk@102855 467b73ca-7a2a-4603-9d3b-597d59a354a9