added bitshift for extract MSB of return code (posix)
added bitshift for extract MSB of return code (posix)

Olivine-Labs/busted,nehz/busted,leafo/busted,istr/busted,o-lim/busted,mpeterv/busted,ryanplusplus/busted,sobrinho/busted,DorianGray/busted,xyliuke/busted