[FIXED JENKINS-18401]

Don't load the plugin classes into plexus.core. This is a quick fix. See my comment in JENKINS-18401 for the proper fix
[JENKINS-18401]

jzlib that artifactory plugin inserts into plexus.core breaks the use of jzlib-1.1.2 in Jenkins 1.519.

hudson.util.IOException2: java.lang.reflect.InvocationTargetException
 	at hudson.maven.Maven3Builder.call(Maven3Builder.java:162)
 	at hudson.maven.Maven3Builder.call(Maven3Builder.java:66)
 	at hudson.remoting.UserRequest.perform(UserRequest.java:118)
 	at hudson.remoting.UserRequest.perform(UserRequest.java:48)
 	at hudson.remoting.Request$2.run(Request.java:326)
 	at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
 	at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
 	at java.util.concurrent.FutureTask.run(FutureTask.java:166)
 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
 	at java.lang.Thread.run(Thread.java:679)
 Caused by: java.lang.Exception: java.lang.reflect.InvocationTargetException
 	at org.jvnet.hudson.maven3.agent.Maven3Main.launch(Maven3Main.java:177)
 	at hudson.maven.Maven3Builder.call(Maven3Builder.java:100)
 	... 10 more
 Caused by: java.lang.reflect.InvocationTargetException
 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
 	at java.lang.reflect.Method.invoke(Method.java:616)
 	at org.codehaus.plexus.classworlds.launcher.Launcher.launchStandard(Launcher.java:329)
 	at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:239)
 	at org.jvnet.hudson.maven3.agent.Maven3Main.launch(Maven3Main.java:174)
 	... 11 more
 Caused by: java.lang.VerifyError: Cannot inherit from final class
 	at java.lang.ClassLoader.defineClass1(Native Method)
 	at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
 	at java.lang.ClassLoader.defineClass(ClassLoader.java:480)
 	at hudson.remoting.RemoteClassLoader.loadClassFile(RemoteClassLoader.java:289)
 	at hudson.remoting.RemoteClassLoader.findClass(RemoteClassLoader.java:229)
 	at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
 	at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
 	at com.jcraft.jzlib.GZIPOutputStream.<init>(GZIPOutputStream.java:46)
 	at com.jcraft.jzlib.GZIPOutputStream.<init>(GZIPOutputStream.java:40)
 	at com.jcraft.jzlib.GZIPOutputStream.<init>(GZIPOutputStream.java:36)
 	at hudson.console.ConsoleNote.encodeToBytes(ConsoleNote.java:174)
 	at hudson.console.ConsoleNote.encode(ConsoleNote.java:193)
 	at hudson.maven.util.ExecutionEventLogger.mojoStarted(ExecutionEventLogger.java:277)
 	at hudson.maven.Maven3Builder$MavenExecutionListener.mojoStarted(Maven3Builder.java:409)
 	at org.apache.maven.lifecycle.internal.DefaultExecutionEventCatapult.fire(DefaultExecutionEventCatapult.java:84)
 	at org.apache.maven.lifecycle.internal.DefaultExecutionEventCatapult.fire(DefaultExecutionEventCatapult.java:42)
 	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:203)
 	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
 	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
 	at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
 	at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
 	at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
 	at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
 	at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:320)
 	at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
 	at org.jvnet.hudson.maven3.launcher.Maven3Launcher.main(Maven3Launcher.java:79)
 	... 18 more