Use SMTInterpol as default solver.
It is the only one that is available in all situations
because it its purely Java.
It also supports rationals+integers and is competitive with MathSAT5,
for interpolation with integers it is even better than MathSAT5.
For -predicateAnalysis-bitprecise and for BMC configurations
MathSAT5 is still used because these configurations require
features that are not supported by SMTInterpol.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14735 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c