Some small classpath tweaks to be compatible with openJDK's api

These were some small classpath changes I found from running the Threadly unit tests within avian.

I will comment in line about each one since they are pretty random.
From http://docs.oracle.com/javase/6/docs/api/java/util/Collections.html#sort(java.util.List): "All elements in the list must implement the Comparable interface. Furthermore, all elements in the list must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the list)."

So we actually should throw a ClassCastException.