RFR (M) 8155951: VM crash in nsk/jvmti/RedefineClasses/StressRedefine: assert failed: Corrupted constant pool

[Coleen Phillimore]

8151066: assert(0 <= i && i < length()) failed: index out of bounds
Summary: lock classes for redefinition because constant pool merging 
isn't thread safe, use method constant pool because constant pool 
merging doesn't make equivalent cpCaches because of invokedynamic

I had to make these changes together.   See bugs for more details.

open webrev at http://cr.openjdk.java.net/~coleenp/8155951/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8155951
bug link https://bugs.openjdk.java.net/browse/JDK-8151066

Tested with rbt nightly test and 24 hours with StressRedefine test.

Thanks,
Coleen