fixes #94

closes #81

Clear constant pool cache entries which are related to
invokehandle/invokedynamic and ones which are unresolved
(have both bytecodes set to 0).

There are two cases when such entries could be non-empty
(have data in f1/f2):
  1. invokedynamic/invokehandle-related entries in which f2 was
     set during constant pool cache initialization.
  2. put/get into static field when class having the field
     is not initialized yet.

Previously, we didn't clear such entries as clearing f2 in
first case results in crash. However, if we don't clear f1
in the second case, we will not be able to initialize class
for the second time (to re-create all enum constants, for
example) as non-empty f2 will cause assertion to fail.

The current implementation uses free bit in constant pool cache
entry to mark all entries with resolved indices (case #1).
The clearing code preserves f2 for all such entries.

Separating changes for $StaticAccessor/$Accessor into separate patch.

In case matching field is not found, clear (set to null) references to faulty DMH.
Long term, should replace such DMH's with instances that will throw more meaningful
error messages at runtime.

Same fix as for static fields, update offset directly
in the DirectMethodHandle$Accessor.

Do not clear f2 in cp cache entry when entry is not initialized yet.
It might be related to invokehandle/invokedynamic, in which case if
we clear f2 it won't be reinitialized.

SystemDictionary doesn't contain anonymous classes.

Starting using Mercurial MQ for managing DCEVM patches.

Making DCEVM to be toplevel project that clones HotSpot repository,
patches the code, builds JVM and tests it.