pdb should try (hard) to avoid creating unnecessary exceptions, e.g. ``AttributeError`` when looking up commands, since this will show up in exception chains then (as "'Pdb' object has no attribute 'do_foo'").

See https://github.com/python/cpython/pull/4666 for an older PR in this regard.

My use case is to display the traceback for exceptions caused within/via Pdb.default(), to see more context when running code from pdb's prompt directly, where currently it would only display the exception itself.