PointsToGraph: add addNode function

I could have do it earlier xD
PointsToGraph: insertDerefPointee optimalization

mess only with nodes instead of pointers. Anyway, adding the pointers
would just add the neighbour node in insert.
PointsToGraph: fix insert

the return value was not set or returned correctly
PointsToGraph: fix and optimalize insertDerefPointer

the method was not doing what it should have. Also use the same
optimalization as in inserDerefPointee
PointsToGraph: change PointsToGraph::forEachFromNode to forEachPointeeOfPointer

that's what I meant to do before, but (somehow :D) mistaken it..