don't let broken RunListener take down the execution.

Based on the following exception we observed:

Aug 31, 2012 1:41:05 PM hudson.model.Executor run
SEVERE: Executor threw an exception
java.lang.NoClassDefFoundError: hudson/plugins/promoted_builds/JobPropertyImpl
	at org.jenkins.plugins.appaloosa.AppaloosaRunListener.onCompleted(AppaloosaRunListener.java:47)
	at org.jenkins.plugins.appaloosa.AppaloosaRunListener.onCompleted(AppaloosaRunListener.java:42)
	at hudson.model.listeners.RunListener.fireCompleted(RunListener.java:178)
	at hudson.model.Run.run(Run.java:1458)
	at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:481)
	at hudson.model.ResourceController.execute(ResourceController.java:88)
	at hudson.model.Executor.run(Executor.java:238)