fixes bvuint in Z3_Backend for long unsigned integer constants
fixes bvuint in Z3_Backend for long unsigned integer constants

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