require git checkout of autostaging for rebuildstaging --deploy

@millerdev I'm pretty ok with this even though it leaves you with autostaging checked out for the following reasons:

- without checking out autostaging, the workflow for testing changes to the fabfile becomes pretty unintuitive—if there are fab changes, especially if someone else is deploying your changes and doesn't specifically think of checking out autostaging first
- `rebuildstaging` without the `--deploy` option still puts you back where you were