Automatically close FSWatcher on error

Closes #3250

lib/fs.js

@@ -659,6 +659,7 @@ function FSWatcher() {
 
   this._handle.onchange = function(status, event, filename) {
     if (status) {
+      self._handle.close();
       self.emit('error', errnoException(errno, 'watch'));
     } else {
       self.emit('change', event, filename);