Upgrade from 2.8.0-rc6 to 2.8.0.

<ChangeLog>

UPGRADE URGENCY: LOW, unless you want to upgrade to new Sentinel code.

• [FIX] Fixed an error in rdbWriteRaw() that should have no practical impact.
• [NEW] Log the new master when SLAVEOF command is used.
• [NEW] Sentinel code synchronized with the unstable branch, the new Sentinel is a reimplementation that uses more reliable algorithms.

</ChangeLog>