Aggregation $sort should correctly handle dates before 1970

> db.foo.insert({d:ISODate('1950-01-01')})

> db.foo.insert({d:ISODate('1980-01-01')})

> db.foo.find().sort({d:1})

{ "_id" : ObjectId("4fc79a7c3c6de6e31566ec2c"), "d" : ISODate("1950-01-01T00:00:00Z") }

{ "_id" : ObjectId("4fc79a7f3c6de6e31566ec2d"), "d" : ISODate("1980-01-01T00:00:00Z") }

> db.foo.aggregate({$sort:{d:1}})

{

	"result" : [

		{

			"_id" : ObjectId("4fc79a7f3c6de6e31566ec2d"),

			"d" : ISODate("1980-01-01T00:00:00Z")

		},

		{

			"_id" : ObjectId("4fc79a7c3c6de6e31566ec2c"),

			"d" : ISODate("1950-01-01T00:00:00Z")

		}

	],

	"ok" : 1

}