Fix following relative URIs in Location

Original code was not working with relative URIs at all,
at least due to `verb` is an HTTP verb, e.g. `:get`. Also,
original code was not handling relative URIs with extension.

Here's problematic redirect flows (that are now properly covered):

##### Redirect to relative URL with filename extension

```
> GET http://example.com
< HTTP/1.1 302
< Location: /index.html

> GET /index.html
```

##### Redirect to relative URL without filename extension

```
> GET http://example.com
< HTTP/1.1 302
< Location: /blog

> GET get://example.com/index
```