build.xml: Fixed accidentially deleted 'junit-' at target test-unit

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13402 b35dd754-fafc-0310-a699-88a17e54d16e
build.xml: Added jar-test-smackx target and let test-unit depend on that, so that clean calls of 'ant test-unit' won't fail.

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@13403 b35dd754-fafc-0310-a699-88a17e54d16e