mongo now transitively uses webapp (because ddp-server does) so we can't
really make an app with mongo and no webapp. This is a bit of a shame
and when we refactor the mongo package we should fix this... but until
then, let's just remove the no-longer-necessary main function and be OK
with this test running a pointless web server.
Specifically, Mongo.Collection objects on the server now have
rawCollection and rawDatabase methods.
You can use MongoInternals.NpmModules.mongodb.version to tell what
version of the mongodb npm module is the backend for HTTP.call. This
version may change incompatibly from version to version of Meteor; use
at your own risk. (For example, we expect to upgrade from the 1.4.x
series to the 2.x series in the not-too-distant future.)
Fixes#3640.
