new package: compression (ported from docker/pkg/archive)

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

vendor/github.com/docker/docker/pkg/longpath/longpath.go

@@ -1,26 +0,0 @@
-// longpath introduces some constants and helper functions for handling long paths
-// in Windows, which are expected to be prepended with `\\?\` and followed by either
-// a drive letter, a UNC server\share, or a volume identifier.
-
-package longpath
-
-import (
-	"strings"
-)
-
-// Prefix is the longpath prefix for Windows file paths.
-const Prefix = `\\?\`
-
-// AddPrefix will add the Windows long path prefix to the path provided if
-// it does not already have it.
-func AddPrefix(path string) string {
-	if !strings.HasPrefix(path, Prefix) {
-		if strings.HasPrefix(path, `\\`) {
-			// This is a UNC path, so we need to add 'UNC' to the path as well.
-			path = Prefix + `UNC` + path[1:]
-		} else {
-			path = Prefix + path
-		}
-	}
-	return path
-}