rust-filepatterns: add comment about Windows path handling
As I replied to the Phabricator message, this is wrong. And I even suspect
it wouldn't compile because of multiple type mismatches.
I think, in Rust where type system is rock solid, we can live with UTF-8
strings except for the bottom storage layer and the top UI/command layer.
We'll still have to get around undecodable characters not to be lost, but
I think it's okay to drop such filenames from match result if they don't
match in UTF-8 world, not in Latin-1 world.
test-convert-git.t
test-subrepo-git.t
test-patchbomb-tls.t