KUrlNavigator: fix handling absolute paths
Make sure that if a user enters an absolute path that it will also be handled as an absolute path and not as a relative path.
We can also start using Utils::concatPaths now instead of manually concatting strings.
Test plan:
- Make sure you have directories /tmp and ~/tmp
- Open e.g. Dolphin at ~/, in the url bar replace all the text with "/tmp", Enter
- It opens ~/tmp even though the user has explicitly requested /tmp
- With this patch it opens /tmp instead
See also other two commits adding tests
See also !921 (merged)
CC @ahmadsamir