test-subrepo: demonstrate problems with subrepo sharing and absolute paths This affects remote paths in .hgsub, as well as clone pooling from a remote source. For reasons unknown, there are stability issues with the relative-path.t tests. If run as a single test, it is stable. If run with --loop, or with -jX for X>1, the hash of the parent repo changes. I'm seeing this on both Windows and Fedora 26. I added an `hg log --debug`, and the manifest hash changes, but I have no idea why.