A simple fix would be adding `assert(e1.appId == e2.appId)` for `SparkListenerApplicationStart`. But actually we can use `===` for well-defined case class directly. Therefore, instead of fixing this issue, I use `===` to compare those well-defined case classes (all fields have implemented a correct `equals` method, such as primitive types)

Author: zsxwing <zsxwing@gmail.com>

Closes #3886 from zsxwing/SPARK-5067 and squashes the following commits:

0a51711 [zsxwing] Use '===' to compare well-defined case class