This is the only operation I'm going to explicitly make a ticket for because it's sufficiently complicated. Once this work is complete, we will have the plumbing for all cursor based operations. We need to do a few things for this one:

• AggregateOperation needs to disambiguate the command construction, and cursor construction
• Cursor needs to be able to accept an operation, and run that instead of ns and cmd
• executeOperation needs to return the selected server so that a cursor can save it for GetMore operations
• GetMore needs to be able to execute with a Server rather than a Topology