Refactor pkg/archive with a platform-independent stat struct

pkg/archive contains code both invoked from cli (cross platform) and
daemon (linux only) and Unix-specific dependencies break compilation on
Windows. We extracted those stat-related funcs into platform specific
implementations at pkg/system and added unit tests.

Signed-off-by: Ahmet Alp Balkan <ahmetb@microsoft.com>

archive/archive_windows.go

@@ -0,0 +1,12 @@
+// +build windows
+
+package archive
+
+import (
+	"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
+)
+
+func setHeaderForSpecialDevice(hdr *tar.Header, ta *tarAppender, name string, stat interface{}) (nlink uint32, inode uint64, err error) {
+	// do nothing. no notion of Rdev, Inode, Nlink in stat on Windows
+	return
+}