fix a bug in static refiner of value analysis, that resulted in precision getting computed but not being put in place; thanks to Pavel for taking note and reporting this issue; made some refactorings along the way

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13466 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c