Improved the tearDown() function so the temporary directory is deleted after the test.
This follows r7026 (http://svn.gna.org/viewcvs/relax?rev=7026&view=rev) and the proposal of Edward
d'Auvergne at: https://mail.gna.org/public/relax-devel/2008-07/msg00038.html (message ID:
7f080ed10807290219m18601df6nf2df7e91848a9680@...).
