Remove FileUtil in favor of FileManager consolidation.

Methods independent of FileManager state are in the companion.

While I was at it, also swapped the sense of diffing check and log,
so that it's more natural (original = check, revised = log).
timings is dead code
inline FileManager.JAVA_OPTS
Consolidate `RunnerManager` & `DirectRunner` as `SuiteRunner`

Test suite arguments now `SuiteRunner` constructor arguments.
`FileManager` instance focusses on managing classpath.