in client_python.cc. This hides the container implementation details from python API, and make datasourceclient usable 'directly'.

Added a bit of optional niftyness to some of the createXXX functions; if you pass it any python object, it'll INCREF it and DECREF it again upon its own destruction. With this, we can make sure some objects don't live past the lifetime of other objects they depend on (in this case iterator, updater and finder, regarding the DataSourceClient they came from)