Passing subdomain: '' to url_for removes the subdomain (instead of adding a leading .)
Adding a boolean route constraint checks for presence/absence of request property
Duplicate options before mutating them
Add url generation tests for #10185
Refactor ActionDispatch::Http::URL.build_host_url

Add support for extracting the port from the :host option and for
removing the subdomain by using nil, false or ''.
Add CHANGELOG entries - closes #10180, #10185