Revise JUnit vs. Spring timeout support in reference manual

Prior to this commit, the discussion of JUnit vs. Spring with regard to
timeout support in tests erroneously claimed that Spring's support for
JUnit's @Test(timeout=...) did not include set up and tear down or
repetitions. This information, however, was based on a previous version
of SpringJUnit4ClassRunner and is no longer valid.

This commit revises the affected section of the testing chapter in the
reference manual accordingly.