Fix issue with watch emitting an event multiple times

Hi Mikeal,

I was using the module to watch a directory and noticed that some events are duplicated. Most commonly 'created' and 'removed'. I've written a small '[test](https://github.com/ggordan/watch/commit/6d671f995d71fed5f0899544a2e1ee8db546e07b)' and ran it on both Ubuntu and Mac and got the same results. 
```javascript
ORIGINAL: /home/ggordan/Dropbox/Sites/watch/test/testFile2 created
ORIGINAL: /home/ggordan/Dropbox/Sites/watch/test/testFile2 created
/home/ggordan/Dropbox/Sites/watch/test/testFile2 created
ORIGINAL: /home/ggordan/Dropbox/Sites/watch/test/testFile2 removed
ORIGINAL: /home/ggordan/Dropbox/Sites/watch/test/testFile2 removed
/home/ggordan/Dropbox/Sites/watch/test/testFile2 removed
```

Have a look and let me know what you think.

Thanks,
Gordan