Replace org.apache.logging.log4j.ThreadContext.clear() with the more precise clearMap().
- [LOG4J2-634] ThrowableProxy ctor throws an exception when using suppressed exceptions.
- [LOG4J2-584] TCP and UDP socket servers should be able to handle JSON log events
- [LOG4J2-583] TCP and UDP socket servers should be able to handle XML log events


git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1594389 13f79535-47bb-0310-9956-ffa450edef68