Change the default in PredicateCPA from approximating bitvectors
with rationals to approximating bitvectors with integers.
This makes much more sense of course.
Floating-point variables are still approximated with rationals.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14736 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c