all: Add filesystem notification support

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3986

vendor/github.com/zillode/notify/tree.go

@@ -0,0 +1,22 @@
+// Copyright (c) 2014-2015 The Notify Authors. All rights reserved.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+package notify
+
+const buffer = 128
+
+type tree interface {
+	Watch(string, chan<- EventInfo, func(string) bool, ...Event) error
+	Stop(chan<- EventInfo)
+	Close() error
+}
+
+func newTree() tree {
+	c := make(chan EventInfo, buffer)
+	w := newWatcher(c)
+	if rw, ok := w.(recursiveWatcher); ok {
+		return newRecursiveTree(rw, c)
+	}
+	return newNonrecursiveTree(w, c, make(chan EventInfo, buffer))
+}