archive: always use portable path component separators with subrepos The previous behavior when archiving a subrepo 's' on Windows was to internally name the file under it 's\file', due to the use of vfs.reljoin(). When printing the file list from the archive on Windows or Linux, the file was named 's\\file'. The archive extracted OK on Windows, but if the archive was brought to a Linux system, it created a file named 's\file' instead of a directory 's' containing 'file'. *.zip format achives seemed not to have the problem, but this was definitely an issue with *.tgz archives. Largefiles actually got this right, but a test is added to keep this from regressing. The subrepo-deep-nested-change.t test was repurposed to archive to a file, since there are several subsequent tests that archive to a directory. The output change is losing the filesystem prefix '../archive_lf' and not listing the directories 'sub1' and 'sub1/sub2'.