Fixes bad href attribute in redirects fallback view

I've written an failing test but unsure how to fix the issue. 
[The problem is tracked to this place](https://github.com/alex-ross/rails/blob/fixes-bad-redirect-fallback-link/actionpack/lib/action_controller/metal/redirecting.rb#L76)
```ruby
self.response_body = "<html><body>You are being <a href=\"#{ERB::Util.unwrapped_html_escape(location)}\">redirected</a>.</body></html>"
```

We are using `unwrapped_html_escape` which will convert all `&` in the query string to `&amp;` inside the href attribute. This will then lead to an invalid query string when a user clicks on the link. For example `&foo=bar` will be `&amp;foo=bar` in the browser and if we redirects to an other application this could cause lots of problems.

I guess `unwrapped_html_escape` is important to fix some other unwanted stuff in the url but is there an way to except the `&` character here without lots of workarounds?