Error when retrieving UTF-8 strings from database

When submitting a news story that has UTF-8 encoded characters in its title, the submission completes successfully but the resulting redirect produces the following error:

```
ArgumentError at /
invalid byte sequence in US-ASCII
```

For some reason, it is falsely assumed that strings returned by Redis are ASCII strings. I have fixed this problem in production by adding the following line to `config.ru`:

```
Encoding.default_external = Encoding::UTF_8
```