Revert "Instead of three separate functions, consolidate to SetStdio()"

This reverts commit faca1846de9ddafcfd2b9e25d5cf67aa130fddc9.
Revert "Configuration tests, which involved wrapping os/exec.Cmd..."

This reverts commit b424ead08d65be2411587b1630ce4552dae79896.
Try a new scheme instead of creating a new interface.