Allow sending files with any status

Fixes #3037. Seems like it was unintentional that `Status#sendFile` only works with `Ok`.

@guillaumebort @jroper
About the form, I would suggest:

```scala
val file = new java.io.File("test.tmp")
file.createNewFile()
val result = Ok.sendFile(file)
file.delete()

(result.header.status aka "status" must_== OK)
  (result.header.headers.get(CONTENT_DISPOSITION) aka "disposition" must beSome(
    """attachment; filename="test.tmp"""")
```