#459 Add a uniqueIndexes method to the relation class

[Rick McGuire]

A uniqueIndexes method would make the relation class easier to use. The allIndexes method shows how to reduce this to a smaller set, but there's no reason why the relation class shouldn't be able to do this directly rather relying on the programmer to remember how to use the set class to reduce this.

[Rick McGuire]

code: [r8295]
test: [r8296]
docs: [r8297]

• status: accepted --> pending
• pending_work_items: code+doc+test --> complete
• milestone: None --> v4.2.0