Improve selection of require packages. bnc#895070. bnc#896178. bnc#896185.

I understand it in the same way. I wanted to prevent another https://bugzilla.novell.com/show_bug.cgi?id=896178 by making clear that whether in the future some other module needs to calculate that list it should ask ```Packages```.

And to be honest, also to fit better in the human readable changelog entry "enabled access to those selections from other yast modules" :-P