Shuffle recv_msg() into the return value for send_msg().
Shuffle recv_msg() into the return value for send_msg().

Additionally, to support the methods where multiple recv_msg() calls
are made (multiple responses), a new method is introduced which does
the upfront request in preparation for the following receives.

basho/riak-python-client,basho/riak-python-client,bmess/riak-python-client,basho/riak-python-client,bmess/riak-python-client,GabrielNicolasAvellaneda/riak-python-client,GabrielNicolasAvellaneda/riak-python-client