Add more options to the InitialStatesFor enum, instead of only exit, one can now also choose to use all exit nodes for each function (or only the entry function) and additionally the loopheads of endless loops (these are explicitly not handled in InitialStatesFor.EXIT)

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14644 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c