RFR (XS) 8066679: jvmtiRedefineClasses.cpp assert cache ptrs must match

[serguei.spit...@oracle.com]

Please, review the fix for:
  https://bugs.openjdk.java.net/browse/JDK-8066679

Open hotspot webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/hotspot/8066679-JVMTI-cache.1/


Summary:

  There can be multiple concurrent RetransformClasses calls on 
different threads.
  So that, the assert "cache ptrs must match" is incorrect as it was 
based on wrong assumptions.
  The fix removes two related asserts and also frees the scratch_class 
cached_class_file_bytes
  if it is necessary to avoid leaking the memory.


Testing:
  In progress: nsk redefine classes tests, JTREG java/lang/instrument


Thanks,
Serguei