org.apache.jorphan.reflect.ClassFinder will return the same classname multiple 
times if that class is located in multiple places in the search path.  

To reproduce, make a copy of ApacheJMeter_core.jar in lib/ext, restart, and 
then add anything to the testplan.  Instead of a single item being added, two 
identical items will be added.

To fix this the list of found classes should be replaced with a Set.  This can 
be kept internal to the class and does not have to affect the public interface.

I verified this problem still exists in cvs as of 8/28.