Should not watch after .close() is called.

Fix yuanchuan#105

lib/watch.js

@@ -231,8 +231,11 @@ Watcher.prototype.close = function(fullPath) {
   // Do not close the Watcher unless all child watchers are closed.
   // https://github.com/yuanchuan/node-watch/issues/75
   if (is.emptyObject(self.watchers)) {
-    this._isClosed = true;
-    process.nextTick(emitClose, this);
+    // should emit once
+    if (!this._isClosed) {
+      this._isClosed = true;
+      process.nextTick(emitClose, this);
+    }
   }
 }
 
@@ -385,6 +388,12 @@ Watcher.prototype.watchDirectory = function(dir, options, fn, counter = nullCoun
       delete opts.recursive;
     }
 
+    // check if it's closed before calling watch.
+    if (self._isClosed) {
+      done();
+      return self.close();
+    }
+
     var watcher = fs.watch(dir, opts);
 
     self.add(watcher, {

test/test.js

@@ -696,6 +696,17 @@ describe('watcher object', function() {
       });
     });
 
+    it('should not watch after .close() is called', function(done) {
+      var dir = tree.getPath('home');
+      watcher = watch(dir, { delay: 0, recursive: true });
+      watcher.close();
+
+      watcher.getWatchedPaths(function(dirs) {
+        assert(dirs.length === 0);
+        done();
+      });
+    });
+
     it('Do not emit after close', function(done) {
       var dir = tree.getPath('home/a');
       var file = 'home/a/file1';
@@ -720,6 +731,7 @@ describe('watcher object', function() {
         }, 100);
       });
     });
+
   });
 
   describe('getWatchedPaths()', function() {