Fix custom URL for admin area and login page

[poetter-sebastian]

If you use a plugin who hides the admin page on a custom url

Plugins like
https://de.wordpress.org/plugins/wp-hide-security-enhancer/
https://de.wordpress.org/plugins/hide-my-wp/
https://de.wordpress.org/plugins/wps-hide-login/

According to #1080 #443

[spleen1981]

• Rather than local preg_matches I would introduce a new qtranxf_get_admin_base function maybe in url.php
• Though the regex looks ok, I would use a simpler str_replace( [site_url(), '/'], '', admin_url() );

[poetter-sebastian]

I've created two new functions for backend and login name and use the str_replace instead of regex.

(maybe the test is not necessary)

[poetter-sebastian]

Thanks for the comments, I simplified the functions.

[herrvigg]

Looks good at first sight, I'll take a closer look soon.

[herrvigg]

I'll try to rewrite this a bit differently.

[poetter-sebastian]

Is there something I can do ?

[herrvigg]

I will merge it, but please test more once it's in master.
I spotted possible bugs but they come from the state before patch so let's separate the scope of changes. Beyond the custom wp-admin functionality coming here, this should also fix neutral path for wp-login.php. The previous version has a regex match against wp-login/ (with trailing slash) but this looks wrong to me. The new check is a strict equality vs wp_login_url() which leads to wp-login.php by default.

[herrvigg]

Released in 3.15.0.