[RFR] Instrumentation for basic Unsafe put/get

[Arthur Eubanks]

webrev:
http://cr.openjdk.java.net/~aeubanks/tsannormalunsafe/webrev.00/index.html

This change adds instrumentation for the interpreter Unsafe implementation,
only for Unsafe_{Get,Put}{Reference,primitive}. Other Unsafe
instrumentation will come later.