merge files
removed deprecated scrapy.conf import

and disable middleware on missing pymongo module
(Re-)Added sharded operation to MongoCacheStorage

allowing to use one Collection per Spider if enabled (old behaviour).
doing trivial API change to MongoClient
Adding support for MongoReplicaSetClient

and some verbosity.
(MongoReplicaSetClient use-case hasn't been tested.)
Allow any positional arguments to MongoClient

Mongo(RS)Client can take any number of arguments, which
don't make sense to filter first, as the user should know best.
Handle database argument in correct order