Replace abstract graph classes.

Introduce new graph class based on two incidence lists.
New function for IncidenceListGraph.

IncidenceListGraph is now reversible.
Remove class ReverseCFG.

Use the reverse-function to reverse the control flow graph.
Add dominator edges.
Separate importers.

Post dominance edges are now imported independently from control
dependence edges.
Separate control dependence graph creation.

Decouple control dependence graph creation from dominator tree creation.
The dominator tree creation process does not determine the dominance
frontiers.
Add new dominator tree creation routines.
Improve control dependence graph creation process.

Control dependence graph are create without explicitly augmenting the
control flow graph. This means we do not need to compute two
post-dominator trees.
Fix control dependence graph creation.
Update dominator tree code.
Remove unneeded iterator.
Merge pull request #40 from a0x77n/dom

Dominator trees