Disable potentially unsafe networking code in log4j.net.

Disables:
* JMSAppender
* JMSSink
* SimpleSocketServer
* SocketHubAppender
* SocketServer

These classes now log an error instead of making network connections.

Their external APIs should remain intact to allow code using them to
migrate without blowing up before runtime, in many cases.

Added tests for the remaining behavior.

Author: lsimons

pom.xml

@@ -179,7 +179,6 @@ Building of NTEventLogappender.dll is disabled. Use an older log4j to get it.
             <include>org/apache/log4j/xml/CustomLevelTestCase.java</include>
             <include>org/apache/log4j/customLogger/XLoggerTestCase.java</include>
             <!-- DefaultInit -->
-            <!-- SocketServer -->
             <include>org/apache/log4j/xml/XMLLayoutTestCase.java</include>
             <include>org/apache/log4j/xml/AsyncAppenderTestCase.java</include>
             <include>org/apache/log4j/varia/LevelMatchFilterTestCase.java</include>