Background: SubTasks were recently added to NextGen projects. These are child tasks to a Story or Task.
Outcome: We'd like to allow bugs to be a child issue underneath a Story or Task.
Motivation: we'd like to associate the bugs directly to the story they relate to (assuming the bug affects just one story/task). This will simplify the management of work in progress and make it clear what's required to close out a story that is active in the sprint.