Handle carriage return (^M)

[tkf]

This should not effect to the data to store. I just need to filter out unused characters including "\r" itself in output stream before inserting it.

See also the PRs for the web interface:

• HTML Notebook carriage-return handling, take 2 ipython/ipython#1674
• Handle carriage return characters ("\r") in HTML notebook output. ipython/ipython#1659

[tkf]

6f3fb3b does not fix ipython/ipython#1674 (comment).

It looks like comint-carriage-motion cannot handle this case.