hookcontext should be able to handle dead units.

[Kapil Thangavelu]

currently the hook context utilizes a current topology to examine nodes. the scheduler however provides for a membership at the time of change, which might include dead units not in the current topology. ensure this case is handled correctly. the settings for the unit are still around, and subsequent scheduled hook execution, will correct the hook awareness of this issue with the correct change event. at minimum though the hook context should behave sensibly in such a case in terms of resolving things.

[Kapil Thangavelu (hazmat)]

The membership is stored on the relation node, this was implemented in the relation-state branch.