Replacing Unsafe.allocateInstance

[Brian Goetz]

> Mocking should be allowed for any class since any class can be mocked. Even
> the JDK ones

An understandable user perspective :)

Unfortunately, many serious security bugs can stem from being able to 
create a bogus instance of a JDK class that is loaded off the 
bootclasspath, and the existence of vectors for creating these exploits 
is a negative for the entire ecosystem.  So, we may need to make some 
tradeoffs between security and convenience.

(Many JDK APIs primarily expose interfaces anyway; these are easily 
mocked without magic.)