Update CHANGES.txt post 0.5.2 release
(cherry picked from commit 422d5d9296fe40ee1ca38aabebf3eeec108673b1)
TEZ-1749. Increase test timeout for TestLocalMode.testMultipleClientsWithSession (Rajesh Balamohan)
(Cherry picked from commit b810c7db18dbe7d43d1df517a556af5e56c507fd)
TEZ-1742. Improve response time of internal preemption (bikas)
(cherry picked from commit 5df90046c494352b55dbffe2fbd6810516d486e7)

Conflicts:
	CHANGES.txt
TEZ-1742. Addendum to fix CHANGES.txt
(cherry picked from commit 8492f10757f9134016f8149f2cc54061d8ddbb0a)

Conflicts:
	CHANGES.txt
TEZ-1742 addendum patch for follow up comments
(cherry picked from commit c6c08c18b77870e71298adb2dc51908473434768)
TEZ-1758. TezClient should provide YARN diagnostics when the AM crashes (bikas)
(cherry picked from commit a2d5768bc274684719dff64b46967264f3d18c0e)
TEZ-1750. Add a DAGScheduler which schedules tasks only when sources
have been scheduled. (sseth)
(cherry picked from commit 67944a1dff87faf3b8bf7ecf3afb1bcda6c43dda)
TEZ-1761. TestRecoveryParser::testGetLastInProgressDAG fails in similar manner to TEZ-1686. (zjffdu)

(cherry picked from commit a7d55e43165cfc570fec6697d80e5ea73d04cf42)