New features and bug fixes:

- 'gvfs prefetch' can now hydrate files as it downloads their blobs
- Added a new 'gvfs service' verb for interacting with the GVFS.Service to mount/unmount all repos
- Reduced the perf overhead of GvFlt notifications for handle creation
- Treat 'git stage' the same as 'git add'
- Gather object and packfile counts in 'gvfs diagnose' to help with perf investigations