Managing ownership in VectorSchemaRoot#addVector, recent changes miss the main fault.

A recent change in VectorSchemaRoot#addVector provided a simple improvement, but completely misses a major shortcoming of this routine and, almost certainly, others like it. Based on the interest in that issue (#301), this issue might be of interest to @axreldable and @jbonofre.

One cannot change the `FieldVector`s belonging to `VectorSchemaRoot`s by simply rearranging the elements of their `List`s without considering the ownership of their underlying buffers. This can cause various problems, particularly when `VectorSchemaRoot`s are closed. This is why `TransferPair` exists.

I would probably need some help with improving this as I'm quite new to using Apache Arrow (and very new to using GitHub). But I have written a possibly improved implementation if this would be of interest and would be open to collaborating on rectifying this bug.

VectorSchemaRoot#addVector から始め、issue #301 の関連する議論を読んでください。FieldVectors の並べ替えが基盤となるバッファの所有権にどのような影響を与えるか、また VectorSchemaRoots を閉じたときにどのように動作するかを調査してください。所有権の移譲が正しく処理され、roots を閉じても説明されているバッファの問題が発生しなくなれば完了です。

索引モデルが issue の本文から書いたものです。