Release notes for MySQL Server and associated products are published in standalone form, not as part of the MySQL Reference Manual. For release notes, see these documents:
MySQL 5.1 Release Notes
MySQL Cluster 7.1 Release Notes
MySQL Connector/ODBC Release Notes
MySQL Connector/Net Release Notes (includes MySQL Visual Studio Plugin release notes)
MySQL Connector/J Release Notes
MySQL Connector/C++ Release Notes
MySQL Proxy Release Notes
MySQL for Excel Release Notes