calculate intervals for cfg (see comment)

[harpend]

intervals is the largest subgraph dominated by the same bb

[harpend]

an interval is the maximal single entry subgraph in which h is the only entry node and which all closed paths contain h. this does not mean h cannot have multiple predecessors or successors it just means there is only one entry node.

[harpend]

added algorithms for creating intervals, need to link to cfg to test

[harpend]

linking done just need to integrate and do testing

[harpend]

works with unit tests