Localize forgot password link

If you are www.site1.com and you click on the forgotten password link, it takes you to www.mainsite.com/wp-login.php?action=lostpassword . This is confusing, as this url as not the same as the one they came from and the users may think that this url is an error. In my tests, if go to www.site1.com/wp-login.php?action=lostpassword it seems to work.

This _should_ be as simple as this

``` php
add_filter( 'lostpassword_url', __NAMESPACE__ . '\\mangle_url', -10, 4 );
```