Implement diff.compareSysStat on windows

and update diff tests to work with slash paths on windows

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

fs/diff_windows.go

@@ -1,14 +1,25 @@
 package fs
 
-import "os"
+import (
+	"os"
+
+	"golang.org/x/sys/windows"
+)
 
 func detectDirDiff(upper, lower string) *diffDirOptions {
 	return nil
 }
 
 func compareSysStat(s1, s2 interface{}) (bool, error) {
-	// TODO: Use windows specific sys type
-	return false, nil
+	f1, ok := s1.(windows.Win32FileAttributeData)
+	if !ok {
+		return false, nil
+	}
+	f2, ok := s2.(windows.Win32FileAttributeData)
+	if !ok {
+		return false, nil
+	}
+	return f1.FileAttributes == f2.FileAttributes, nil
 }
 
 func compareCapabilities(p1, p2 string) (bool, error) {