Vagrant file, ref #59

This it what I've come up with a Vagrantfile so far, though it needs boxes for other operating systems.

* Install [Vagrant](http://www.vagrantup.com/) and VirtualBox
* Run `vagrant up`
* It's now possible to run tests against a Linux box with `vagrant ssh -c 'go test -v ./...'`

I saw one test failure, it may be related to #57 or the use of symlinks. If it's a timing issue, it happened every time. 

```
--- FAIL: TestFsnotifyDeleteWatchedDir (0.51 seconds)
	fsnotify_test.go:471: event received: "_test/TestFsnotifyEventsExisting.testfile": DELETE
	fsnotify_test.go:487: did not receive at least 2 delete events, received 1 after 500 ms
```

Mind you, I see similar test failures on my host OS (OS X).