test-strip: display more information highlight buggy behavior When using `hg strip --keep` on a set of changeset that contains a merge, the set of file considered when rebuilding the dirstate is missing files updated by changeset that are not directly inside the `new-parent::old-parent` range. We start with updating the test with new output highlighting the issue. This issue was spotted because that dirstate inconsistency made the test flaky. The new command make the test less flaky (but still wrong).