added proof reconstructon for Z3,
added certificates for simpler re-checking of proofs (no need to invoke external solvers),
added examples and certificates for all examples,
removed Unsynchronized.ref (in smt_normalize.ML)

(benchmark Isabelle

:assumption (not (= (bvsub bv11[8] bv27[8]) (bvneg bv16[8])))

:formula true

)