receive_code() now reads error message off wire.

4 year old bug finally triggered. If an operation that used
receive_code(int) (e.g. a delete operation) received a
RpbErrorResp from riak, it would not read it from the wire and
the connection would ultimately get reused causing a failure.
bumped pom to 1.4.4-SNAPSHOT
Merge pull request #351 from basho/gh350-pb-get-code-bug

receive_code() now reads error message off wire.