Improve group selection semantics

Now that the last commit tried to avoid changing the child selections if
the selected group partially matched, we should always [un]select all
children when we actually decide to change something.

Before, it would try to minimize selection damage by stopping
[un]selecting when it hit a child that already matched the selection,
but since we minimize damage differently, the all-or-nothing approach is
better, and gets us sane behavior when the group is collapsed.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>