- This doesn't compile right now.
- The nested class ItemData doesn't do anything useful or
meaningful that having model items with the right data wouldn't.
Root is always selected, can't be unselected, and has its own explicit
constructor and name. This resolves issue reported where unchecking
all *visible* groups caused the root to be unchecked, after which
hidden-but-still-selected subgroups were not installed.
Reported by crazy@
If a subgroup is hidden, then it should be considered
selected if its parent is selected or partially-selected.
If the parent group is totally unselected, then the hidden
subgroup shouldn't be installed either. This allows putting
required-packages into a group, without cluttering the
interface.
FIXES#864
