Reduce class loading synchronized contention

In large multithreaded deployment with many annotators, measurements showed large slowdown in class loading as 100's of annotator classes were loaded, perhaps in 100's of instances. Each load operation locked 1 shared global lock. Java 7 implements a finer grained locking for this, so that the lock is per [ classloader + class-name ], to reduce lock contention. This code will need to be conditional for Java 7 and later. See http://docs.oracle.com/javase/7/docs/technotes/guides/lang/cl-mt.html