C++: Check in release that the correct author is set in git

We should check if the correct author to sign the release tarball is set as the git author. Not sure how we can detect that but I already run twice into the problem that the git author was not the same as I signed the tarball with and the release script aborted half-way. This was not catched in the dry-run mode.

**Reporter**: [Uwe Korn](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=uwe) / @xhochy

_{**Note**: *This issue was originally created as [PARQUET-912](https://issues.apache.org/jira/browse/PARQUET-912). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

まずリリーススクリプトを見つけ、通常パスと dry-run パスを比較します。その際、tarball に署名する前に git の作者が確認される箇所に注目してください。誤った作者が release が中止される前に検出され、dry-run モードでも同じ問題を検出できれば完了です。

索引モデルが issue の本文から書いたものです。