several things for impact-like refinement for value analysis (still work-in-progress)

updating impact refiner for value analysis (to be obsolete soon)
adds a reimplementation that also works with multiple error path
added (marker) inferface for unsound refiners
added case for refinement loop in CEGAR algorithm to allow restart of exploration in case no target was found (analysis might be unsound, therefore, at least one more interation is needed to prove safety)

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@12994 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c