RFC: loosening file name limits

[Stefan Monnier]

> must be unicode
> must not contain \\ and various other unportable characters
> must serialise cleanly within our various storage formats
[...]
> We don't guard against many other user-code portability issues like
> having "README" and "Readme" in a single dir; I think we should get rid
> of the second constraint in favour of a nag/warn system where unportable

This is especially true given that Bazaar encourages Free Software: it's
fine to support proprietary OSes, but imposing restrictions under Free
Software OSes because of proprietary ones seems backward.


        Stefan