tree may be mutated when serialized.

This was originally suggested by Guido, discussed on the stdlib-sig mailing
list, and given the OK by Guido directly to me. What this change essentially
means is that Python has taken a policy of silencing warnings that are only
of interest to developers by default. This should prevent users from seeing
warnings which are triggered by an application being run against a new
interpreter before the app developer has a chance to update their code.

Closes issue #7319. Thanks to Antoine Pitrou, Ezio Melotti, and Brian Curtin
for helping with the issue.

r77400.

classes.  Patch by Florent Xicluna.

Florent Xicluna).

renaming of `cPickle` to `pickle`.  The warning was annoying since there's
no alternative to cPickle if you care about performance.  Patch by Florent
Xicluna.

mistake. ( It may come in for sure tough)

Florent Xicluna.

information if a failure happens.

This also simplifies the Cmd.get_names() method implementation; it was written
at a time where dir() didn't consider base class attributes.

Small fixes to test_cmd: fix signature of do_shell, remove duplicate import, add option to run the custom Cmd class.

when using the -3 flag.  Patch by Florent Xicluna.