[Python] C++ API plumbing for returning generic instance of ipc::RecordBatchReader to user

[asfimport]

Currently we have no mechanism of wrapping a std::shared_ptr<arrow::ipc::RecordBatchReader> like we do with some other Arrow types

Reporter: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-1042. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
We do have a RecordBatchReader on the Python side now.