This test covers the case where a local stack slot is first used to
store an object reference and later to store a subroutine return
address. Unfortunately, this confuses the VM's stack mapping code;
I'll be working on a fix for that next.
The new test requires generating bytecode from scratch, since there's
no reliable way to get javac to generate the code we want. Since we
already had primitive bytecode construction code in Proxy.java, I
factored it out so we can reuse it in Subroutine.java.
Compiling the entire OpenJDK class library into a bootimage revealed
some corner cases which broke the compiler, including synchronization
in a finally block and gotos targeting the first instruction of an
unsynchronized method.
