mikel/mail — pull request #760 by grosser (2014-07-29 00:44:11+00:00)
Title: unkown/broken encoding should be binary, not text/plain

this seems wrong and leads to users trying to open weird file in their text-editor
```
Mail::ContentTypeField.new("; name=\"logs.zip\"").to_s
=> text/plain
```

not sure what you think about this ...

@jeremy @bf4