discovery: document the `devel.discovery.randomize` option Gratuitous improvement as I was passing by this config section to add more. Differential Revision: https://phab.mercurial-scm.org/D9797

shelve: move listshelves() to new ShelfDir class, so caller need not pass vfs Differential Revision: https://phab.mercurial-scm.org/D9744

shelve: also create class representing whole directory of shelves It's a little annoying to have to create and pass in a vfs into `listshelves()`. This patch attempts to start addressing that by creating a class that represents a directory containing shelves (the directory can be either `.hg/shelved/` or `.hg/shelve-backup/`). Differential Revision: https://phab.mercurial-scm.org/D9743

shelve: add a method for deleting shelf to new shelf class This is not necessary for my future changes, but it's more consistent to encapsulate the knowledge of the various files in the `Shelf` class. Differential Revision: https://phab.mercurial-scm.org/D9742

shelve: inline ".patch" constant now that it's only used in the Shelf class Differential Revision: https://phab.mercurial-scm.org/D9741

shelve: use listshelves() in cleanupoldbackups() With this patch, there are no more assumptions outside the `Shelf` class about which files (`.patch`, `.hg`, `.shelve`) make up a shelf. As such, this finishes the preparations for making phase-based shelve (perhaps optionally) not write the `.patch` and `.hg` files. Differential Revision: https://phab.mercurial-scm.org/D9740

shelve: make listshelves() list shelves in a given vfs Differential Revision: https://phab.mercurial-scm.org/D9739