New functionality useful for debugging

This is just a quick note that the Function class now has two new methods
for directly viewing the CFG of a function being worked on. This is
useful in a debugger, where allows you to just say:

call F->viewCFG()

and a window will pop up with the function in it, with each basic block
broken into a node in the graph. This requires having 'dot' and 'gv' in
your path.

The two new methods are described here: