RFR: Full GC should cleanup earlier/bad version of redefined classes

[Zhengyu Gu]

Tests suggest that it expects that earlier versions of redefined 
classes, or classes with errors should be cleaned up during full GC cycles.

Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/fullgc_class_unload/webrev.00/

Test:
   tier3_gc_shenandoah.

Thanks,

-Zhengyu