[C++] Document that shared_ptr returned by RecordBatch::column needs to be retained

[asfimport]

I ran into an issue where a now-temporary column was being deferenced, causing a segfault. In older versions of Arrow, the RecordBatch internally retains boxed arrays. We might separately consider returning to this internal data model even though it results in worse IPC performance in some cases.

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-1494. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
PR: #1065

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1065
#1065