Unicode support in log messages and file names

[Andrey]

> As you have seen in http://www.selenic.com/mercurial/bts/issue156
> I always got distracted by other topics for too many months now.
>
> Feel free to provide something for encoding log messages, but
> encoding file names is a different topic and needs discussion.
>
> Thomas

Yes, encoding messages seems much more easy to implement. I'm planning to do 
it like this:
- decode user provided log messages from locale encodeded byte strings to 
unicode strings;
- use terminal encoding to display those messages (provided as unicode 
strings);
- encode log messages (provided as unicode string) in UTF-8 when storing;
- decode log messages from UTF-8 to unicode string when retrieving;
- (the most complex part) make sure switching from byte strings to unicode 
strings does not break thinks.

Is this list OK?