Update CHANGES.txt post 0.5.2 release
Fixing CHANGES.txt for TEZ-1749
TEZ-1742 addendum patch for follow up comments
TEZ-1758. TezClient should provide YARN diagnostics when the AM crashes (bikas)
TEZ-1750. Add a DAGScheduler which schedules tasks only when sources
have been scheduled. (sseth)
TEZ-1761. TestRecoveryParser::testGetLastInProgressDAG fails in similar manner to TEZ-1686. (zjffdu)