Watchman

[fixes #2226]

* currently hard-coded to use watchman. It will only work on `*nix` and wont support windows.
* polling is currently entirely disabled so virtual box users will have issues.

To use:

use node `v0.11.x`

use this branch:

```
npm install --save-dev stefanpenner/ember-cli#watchman
```

 install watchman:

```sh
brew install watchman
```

docs: https://facebook.github.io/watchman/

- [x] auto-detect either in broccoli-sane-watcher or sane itself
- [x] confirm this is good.
- [ ] wait for sane to release

Commenters reporting issues, please provide:

```
node version
watchman version
ember-cli version
OS version:
```
move to rich object that fulfills with meaningful info.