Used for extracting:
- when used asking for a scheme, it will return CURLUE_NO_SCHEME if the
stored information was a guess
- when used asking for a URL, the URL is returned without a scheme, like
when previously given to the URL parser when it was asked to guess
- as soon as the scheme is set explicitly, it is no longer internally
marked as guessed
The idea being:
1. allow a user to figure out if a URL's scheme was set as a result of
guessing
2. extract the URL without a guessed scheme
3. this makes it work similar to how we already deal with port numbers
Extend test 1560 to verify.
Closes#13616
