Fix for Codeception issue #1510 - site-root relative paths

Using a site-root relative path for a form's action fails if PhpBrowser
is configured with a 'url' basepath with a subdir (e.g.
localhost/subdir)
I'd be happy to change it to that - there are other possible scenarios though (which is why I do prefer either using the exact string as passed, or using an API for this that handles all scenarios correctly):

http://user@example.com or
http://user:pass@example.com

Would you prefer those possibilities be left out, or build them in?  I can't think of any other scenarios off the top of my head, can you?