Package groups are not supported by the current pactree recursive method

For groups like `xfce4` and `xfce4-goodies`, we need to use this command to get all of the packages:

```shell
$ pacman -Sg xfce4 | awk '{print $2}'
```

---

For `base` and other metapackages, we need `pactree`. For regular packages, `pactree` can be used also.