Move YARN-3493 in CHANGES.txt from 2.8 to 2.7.1

hadoop-yarn-project/CHANGES.txt

@@ -298,9 +298,6 @@ Release 2.8.0 - UNRELEASED
     YARN-3021. YARN's delegation-token handling disallows certain trust setups
     to operate properly over DistCp. (Yongjun Zhang via jianhe)
 
-    YARN-3493. RM fails to come up with error "Failed to load/recover state" 
-    when mem settings are changed. (Jian He via wangda)
-
     YARN-3136. Fixed a synchronization problem of
     AbstractYarnScheduler#getTransferredContainers. (Sunil G via jianhe)
 
@@ -465,6 +462,9 @@ Release 2.7.1 - UNRELEASED
     YARN-3434. Interaction between reservations and userlimit can result in 
     significant ULF violation (tgraves)
 
+    YARN-3493. RM fails to come up with error "Failed to load/recover state"
+    when mem settings are changed. (Jian He via wangda)
+
 Release 2.7.0 - 2015-04-20
 
   INCOMPATIBLE CHANGES