This PR refactors all of the methods on `Vfs` from accepting `&mut self` to
accepting `&self` and keeping data wrapped in a mutex. This builds on previous
changes to make reference count file contents and cleans up the last places
where we're returning borrowed data out of the VFS interface.
Once this change lands, there are two possible directions we can go that I see:
* Conservative: Refactor all remaining `&mut Vfs` handles to `&Vfs`
* Interesting: Embrace ref counting by changing `Vfs` methods to accept `self:
Arc<Self>`, which makes the `VfsEntry` API no longer need an explicit `Vfs`
argument for its operations.
* Change VfsFetcher to be immutable with internal locking
* Refactor Vfs::would_be_resident
* Refactor Vfs::read_if_not_exists
* Refactor Vfs::raise_file_removed
* Refactor Vfs::raise_file_changed
* Add Vfs::get_internal as bits of Vfs::get
* Switch Vfs to use internal locking
* Migrate all Vfs methods from &mut self to &self
* Make VfsEntry access Vfs immutably
* Remove outer VFS locking (#260)
* Refactor all snapshot middleware to accept &Vfs instead of &mut Vfs
* Remove outer VFS Mutex across the board
This one took a little bit of tracking down; the VfsWatcher used to spawn a new
thread and then stall/park forever. With one of the recent changes to get rid of
the extra thread, VfsWatcher started getting dropped, which in turn dropped the
watchers created by the notify crate.
Because the threads only tie back to the VfsWatcher was a cloned
Arc<Mutex<VfsSession>>, everything was fine, except that their mpsc::Receiver
objects were no longer receiving events.
This manifested itself as the file watcher magically not watching any files.
Oops.
* Moved commands into their own folder to reduce `bin.rs`'s size
* Moved all of the VFS-related functionality into its own folder
* Documented a lot of functions, including a few very obscure ones
