made Z3 Backend handle large constanst (>32bit) better
made Z3 Backend handle large constanst (>32bit) better

* bvbin, bvhex and bvuint should work now
* bvsint not working yet
* parsing results larger than 64 bits still does not work

finnhaedicke/metaSMT,finnhaedicke/metaSMT,nbruns1/metaSMT,hoangmle/metaSMT,agra-uni-bremen/metaSMT,hoangmle/metaSMT,nbruns1/metaSMT,agra-uni-bremen/metaSMT,nbruns1/metaSMT,hoangmle/metaSMT,agra-uni-bremen/metaSMT,finnhaedicke/metaSMT