Fixed compiler so that it reuses already generated OptimizerNodes within the recursive descent step of the GraphCreatingVisitor by passing down the current con2node state. This implies that one has to consider the root of the step function for computing the unclosed branch stack and for merging the branch plan maps. The method hasDamOnPathDownTo had also been adjusted for the step function, otherwise the "Tracing dams for deadlock detection is broken" compiler exception is thrown.