Support nested properties (fix for oplog field filtering)
Support nested properties (fix for oplog field filtering)

_pop_excluded_fields doesn't support nested $set/$unset operations yet,
this needs to be fixed still like in _copy_included_fields

sailthru/mongo-connector,mongodb-labs/mongo-connector,mongodb-labs/mongo-connector,sailthru/mongo-connector,ShaneHarvey/mongo-connector,10gen-labs/mongo-connector,ShaneHarvey/mongo-connector,10gen-labs/mongo-connector