an option to print slash instead of backslash for stat

[Alexis S. L. Carvalho]

Thus spake Alexis S. L. Carvalho:
> I'm not completely opposed to this (running tests with pysh would
> probably benefit A LOT from something like this), but I think a "slash"
> option in the [ui] section would be better - maybe always using slashes
> would be even better, but I don't think all users would be happy if we
> do that...
> 
> And it looks like it wouldn't be too hard to add this setting...

I've pushed to crew a set of changes that allows you to use

[ui]
slash = True

in your .hgrc to print most paths with "/", even on windows.

I think this should cover most regular messages, but some error messages
that print absolute paths may still use a mix of "\" and "/".

If you use this option and see a _regular_ message that uses "\", please
report it (I can't guarantee it's going to be fixed, but I'd like to at
least know these places).

Alexis