Spills

I have decided to use the VirtRegMap class in order to place the spill code. I have been working on this yesterday, and today. The main problem is that I had to change much of my data structures to accommodate the creation of new virtual registers. For example, the interference graph now looks like this. Besides this, I have not been able to put the whole code running. But I know where the bugs are (I know some of them - no one knows all of them).