Code review comment for lp:~vexo/bzr/fix-1123460

Thanks for noting the previous merge request. I will look into
marking it "duplicate" or "invalid", etc. Did you notice John
Meinel's suggestion to decode the utf-8 to unicode? Does that still
apply? I'm still learning about unicode vs. utf-8, etc.

Do we need to worry about unicode format string for
bzrlib/log.py:format_signature_validity:339 ? How about translations
of these format strings and the two format strings in
bzrlib/log.py:format_signature_validity:341,343?