Provide a new possibility to iterate through ARGPaths
that is easier to use and clearer in respect to the relation between
states and edges
instead of the existing iterator for Pair<ARGState,CFAEdge>.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13148 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c