Arch Group Packages Need Expanding

[ripytide]

At the moment if you put a group package in you group files for the arch backend then pacdef cannot detect that it is a group (via pacman -Sg <package_name>) and yet when querying packages each package group member is itself explicit (unlike the meta-package approach). To fix this I think we just need to detect and expand packages which are groups with pacman -Sgq <package> and then list those as the managed packages instead of the raw packages given in the group files.