as the death entries of a deceased processes that were in this group
and have not yet been reaped hold references to the group, so that it
won't be deleted until the group is empty and all gone group members
have been reaped. This fixes #1799 at last.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@24335 a95241bf-73f2-0310-859d-f6bbb57e9c96