shelve: replace repo instance in Shelf class by vfs instance I'd like to be able to teach the `Shelf` class to read shelves from `.hg/shelve-backup/` in addition to `.hg/shelved/`. That means that we'll have to pass in a vfs instead of the repo, so this patch does that preparation. Differential Revision: https://phab.mercurial-scm.org/D9738

shelve: use listdir() instead of readdir() when we don't need stat information Differential Revision: https://phab.mercurial-scm.org/D9737

shelve: don't crash on file with unexpected extension in .hg/shelved/ We assumed that the files in the `.hg/shelved/` directory have an extension. That's a valid assumption except that users may put garbage in the directory. This patch fixes the crash by simply not assuming that the result of splittin a string at '.' yields an extension. We don't use the extension since the previous patch anyway. Differential Revision: https://phab.mercurial-scm.org/D9720

shelve: don't include invalid shelves in `hg shelve --list` Before this patch, if a shelved change is missing its `.hg` file, we still list it in `hg shelve --list`, but then `hg unshelve` crashes. This patch makes it so we only list valid shelved changes. This patch means that users who do `touch .hg/shelve/buy-milk.patch` as a form of TODO list will no longer see their TODO items in `hg shelve --list`. Differential Revision: https://phab.mercurial-scm.org/D9719

shelve: extract some repeated creation of shelf instances to variables This just looks cleaner to me; I'd be surprised if there's any measurable performance improvement. Differential Revision: https://phab.mercurial-scm.org/D9714

shelve: teach new shelf class to check if .shelve file exists This removes the only remaining use for `shelvedfile`, so the class now goes away. Differential Revision: https://phab.mercurial-scm.org/D9713

shelve: move method for creating backup to new shelf class Differential Revision: https://phab.mercurial-scm.org/D9712