adding new property into results.py for handling overflows.
adding new property into results.py for handling overflows.

The property is used for "signed integers overflow",
which is undefined behavior in ISO-C-standard.

Currently no verifier/tool supports this property, but maybe soon.
Therefore BenchExec should support it first.

ultimate-pa/benchexec,dbeyer/benchexec,martin-neuhaeusser/benchexec,martin-neuhaeusser/benchexec,martin-neuhaeusser/benchexec,dbeyer/benchexec,ultimate-pa/benchexec,IljaZakharov/benchexec,sosy-lab/benchexec,IljaZakharov/benchexec,michkot/benchexec,martin-neuhaeusser/benchexec,sosy-lab/benchexec,michkot/benchexec,ultimate-pa/benchexec,IljaZakharov/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,IljaZakharov/benchexec,dbeyer/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,michkot/benchexec,dbeyer/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec