handle error code > 128 in system_raw like system_piped

some shells, such as csh and fish, return a different exit code format
from sh, bash, which subprocess.call doesn’t properly transform.
test exit code with csh

if available, because csh exit codes can differ from sh/bash
Merge pull request #6006 from minrk/ec128

handle error code > 128 in system_raw like system_piped