Directory::onDidChange / File::onDidChange fire twice on file save if file not empty

_From @paulpflug on June 22, 2015 9:58_

``` coffee
console.log "watching"
fired = false
entry.onDidChange ->
  console.log "fire"
  unless fired
    fired = true
    console.log "real fire"
    setTimeout (->fired = false), 1000
```

Output:

```
watching
## saving empty file
fire
real fire
## saving file with content
fire
real fire
fire
```

_Copied from original issue: atom/atom#7363_
