Added the def_system_command stuff back, so that the built-in shell's cd would actually have an effect on the commands that the shell subsequently executes.
Added the def_system_command stuff back, so that the built-in shell's cd would actually have an effect on the commands that the shell subsequently executes.

bsoetaer/system-programming-ruby,bsoetaer/system-programming-ruby,bsoetaer/system-programming-ruby