API change: relation-broken hook context

[William Reade]

On Thu, 2011-12-08 at 18:09 -0500, Kapil Thangavelu wrote:
> the rel hook even for rel-broken is distinct enough that i'd rather see an 
> additional rel hook derived context for broken. Some uses, being able to know 
> for example the name of the relation so it can reference associated resources, 
> or look at what settings the unit had established for the relation so it can do 
> proper cleanup.
> 
> regarding the additional api mapping of a rel hook context to a rel broken 
> hook context.. i'd go with
> 
> get-members -> empty set
> get relation settings of related unit -> error no such unit.
> get relation settings of self unit -> works as normal
> set setting relation setting of self -> error
> 
> cheers,
> 
> Kapil

Sounds good to me.