Add MarkerManager.clear() for proper and sane testing. Also prefix test methods with "test" instead of using the postfix "Test".

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1593268 13f79535-47bb-0310-9956-ffa450edef68
Document empty block.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1593269 13f79535-47bb-0310-9956-ffa450edef68