Support the creation of top-level folders on Windows (fixes #1822)

internal/osutil/mkdirall.go

@@ -0,0 +1,17 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+// +build !windows
+
+package osutil
+
+import (
+	"os"
+)
+
+func MkdirAll(path string, perm os.FileMode) error {
+	return os.MkdirAll(path, perm)
+}