rust-filepatterns: use literal b'#' instead of cast

rust-filepatterns: fix type of warnings tuple to (bytes, bytes) Otherwise warn() in match.py would fail if the warning contains non-ASCII character. We might want to add a thin ByteString wrapper around Vec<u8> to implement ToPyObject<ObjectType = PyBytes>, but I'm not sure.

hgignore: add escape syntax test for glob patterns The last example, [\#], is what the rust implementation fails to parse. The other escapes can be removed by regexp engine or _globre().