Polish xdg-realpath
I didn't leave xdg-realpath in the cleanest of conditions, this fixes it by:
- making its behavior consistent across call modes
- moving it closer to the "real"
realpath
- Answer some questions about edge cases in the docs.
- Add tests for xdg-realpath
Fixes #260
Includes the patch from !119, which was needed for testing.
Edited by Slatian