unsafe-mock: a copy of Unsafe from the most recent JDK

This library provides a current version of sun.misc.Unsafe that supports all APIs up through the new "fences" API in Java 8 EA builds b71 and later. This Unsafe is a copy of the one from Java 8 EA build b71, and it is expected that if you want to build against it you put it in javac's bootclasspath. You are responsible for determining in your own code whether you can access Unsafe and which methods are available; this library is only to provide an all-inclusive Unsafe against which you can compile.