modify xml decoders so additionalProperties override existing properties (allows, for example, the ability to load a set of saved events into a new tab in chainsaw, because chainsaw can modify the application/hostname properties that control event routing). Also fixed a bug in additional properties loading.
logging/log4j/companions/receivers/trunk/src/main/java/org/apache/log4j/xml/UtilLoggingXMLDecoder.java