sftp: add required packages to vendor

vendor/github.com/kr/fs/filesystem.go

@@ -0,0 +1,36 @@
+package fs
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// FileSystem defines the methods of an abstract filesystem.
+type FileSystem interface {
+
+	// ReadDir reads the directory named by dirname and returns a
+	// list of directory entries.
+	ReadDir(dirname string) ([]os.FileInfo, error)
+
+	// Lstat returns a FileInfo describing the named file. If the file is a
+	// symbolic link, the returned FileInfo describes the symbolic link. Lstat
+	// makes no attempt to follow the link.
+	Lstat(name string) (os.FileInfo, error)
+
+	// Join joins any number of path elements into a single path, adding a
+	// separator if necessary. The result is Cleaned; in particular, all
+	// empty strings are ignored.
+	//
+	// The separator is FileSystem specific.
+	Join(elem ...string) string
+}
+
+// fs represents a FileSystem provided by the os package.
+type fs struct{}
+
+func (f *fs) ReadDir(dirname string) ([]os.FileInfo, error) { return ioutil.ReadDir(dirname) }
+
+func (f *fs) Lstat(name string) (os.FileInfo, error) { return os.Lstat(name) }
+
+func (f *fs) Join(elem ...string) string { return filepath.Join(elem...) }