RFR(M): optional flattening - interpreter/runtime part

[Frederic Parain]

Greetings,

Please review this changeset implementing optional field flattening
in the interpreter and the runtime. The support for C2 is provided by
Tobias in a separate changeset.

http://cr.openjdk.java.net/~fparain/optional-flattening-interp/webrev.00/index.html

Note that trying to run some programs/tests with this changeset and
not Tobias’ changeset is likely to cause crashes unless interpreted mode
is forced and passing/returning values in registers is disabled.

Thank you,

Fred