Path-style addressing requires region

Using `https://s3.amazonaws.com/mybucket/puppy.jpg` only works for US Standard region. Other regions fail with:

```
<Error>
  <Code>PermanentRedirect</Code>
  <Message>The bucket you are attempting to access must be addressed using the specified endpoint. Please send all future requests to this endpoint.</Message>
  ...
```
The correct URI is `https://s3-eu-west-1.amazonaws.com/mybucket/puppy.jpg`.