Handle destination directory being /.

When the destination directory is `/` and no files were specified (because we want all files), an error was thrown because we were attempting to symlink the already existing temp directory (which was created by `quick-temp` in `broccoli-writer`).

* Add basic tests illustrating the issue.
* Add JSHint.
* Create basic test for file globbing (to ensure no regressions from this change).

@linstula & @rwjblue