Cmd used to blindly chop off the last character of every input line.  If
the input reached EOF and there was no final new line, it would truncate
the last character of the last command.  This fix instead strips trailing
\r\n from the input lines.  While this is a small behavior change, it
should not break any working code, since feeding a '\r\n' terminated
file to Cmd would previously leave the \r's on the lines, resulting
in failed command execution.

I wrote the unit test in preparation for a PyOhio TeachMe session
run by Catherine Devlin, and we can thank Catherine and the PyOhio
session attendees for the fix.  I've added Catherine to the Acks file
for organizing and leading the TeachMe session, out of which we will
hopefully get some new contributors.