New aggregation framework support

[flaper87]

Even if it's still unstable, we should start implementing the new aggregation framework. This implementation should replace the map/reduce one.

[emperorcezar]

I hear it can give almost join support, but I haven't really looked into it yet.

[flaper87]

Sort of, Posting the doc's link for future reference.

http://www.mongodb.org/display/DOCS/Aggregation+Framework

[jonashaag]

Is this supported by PyMongo yet?