Add "throws SolverException" to RegionManager.entails().
BDD packages are not supposed to fail for such a method,
but we have an implementation that is backed by an SMT solver,
and this may fail.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14255 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c