Added some code for computing the live variables during the cfa creation. The computation can be toggled via "cfa.findLiveVariables=true". The information about the live variables is stored in the cfa object.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14447 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c