don't execute fs check if the user has recent activity

The check could be expensive with some backends and is generally
only required the first time that a user logs in

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

vfs/vfs.go

@@ -73,7 +73,6 @@ type Fs interface {
 	Rename(source, target string) error
 	Remove(name string, isDir bool) error
 	Mkdir(name string) error
-	MkdirAll(name string, uid int, gid int) error
 	Symlink(source, target string) error
 	Chown(name string, uid int, gid int) error
 	Chmod(name string, mode os.FileMode) error