org.jnode.vm.compiler.ir.RegisterPool

Hi!

I think the current implementation is just too weak to support some complex CPU like a X86.

I'd like to add the following methods to org.jnode.vm.compiler.ir.RegisterPool:

// check whether a register is already allocated
public abstract bool isInUse(Object register);

// require a particular register (returns false on failure)
public abstract bool request(Object register);

There are a few more features that may be useful, but they are less important (yet):
* associate each required register with an object (to be able to find out who/where the register is allocated
* allow multiple allocations of one register (keep a reference count)

Because any of these changes will broke existing code, I prefer to discuss them before changing anything!

-Patrik