BMC+induction: Added an option to switch off/on the generation of additional invariants by the induction process. In the future, this behavior should be encapsulated by the InvariantGenerator mechanism, but some refactoring is required first.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13274 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c