UnitKit: switch printf's to NSLog's. We can't mix NSLog and printf because in some cases they are buffered differently and the order gets mixed up (e.g. on Travis CI) - and it's critical that test failures are printed at the right place in the log output

git-svn-id: http://svn.gna.org/svn/etoile/trunk/Etoile/Frameworks/UnitKit@10069 7b3f36aa-e6db-49c1-8b4c-66eac1997e64