Update CHANGES.txt to set the release date for 2.5.1

(cherry picked from commit 17ffbe08642c622f099dd1cd9cb9e008ba98ea52)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -463,7 +463,7 @@ Release 2.6.0 - UNRELEASED
     HADOOP-11083. After refactoring of HTTP proxyuser to common, doAs param is 
     case sensitive. (tucu)
 
-Release 2.5.1 - UNRELEASED
+Release 2.5.1 - 2014-09-05
 
   INCOMPATIBLE CHANGES
 

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -496,7 +496,7 @@ Release 2.6.0 - UNRELEASED
     HDFS-7042. Upgrade fails for Windows HA cluster due to file locks held during
     rename in JournalNode. (cnauroth)
 
-Release 2.5.1 - UNRELEASED
+Release 2.5.1 - 2014-09-05
 
   INCOMPATIBLE CHANGES
 

hadoop-mapreduce-project/CHANGES.txt

@@ -130,7 +130,7 @@ Release 2.6.0 - UNRELEASED
     MAPREDUCE-6070. yarn.app.am.resource.mb/cpu-vcores affects uber mode but
     is not documented (Tsuyoshi OZAWA via jlowe)
 
-Release 2.5.1 - UNRELEASED
+Release 2.5.1 - 2014-09-05
 
   INCOMPATIBLE CHANGES
 

hadoop-yarn-project/CHANGES.txt

@@ -300,7 +300,7 @@ Release 2.6.0 - UNRELEASED
     YARN-2534. FairScheduler: Potential integer overflow calculating totalMaxShare. 
     (Zhihai Xu via kasha)
 
-Release 2.5.1 - UNRELEASED
+Release 2.5.1 - 2014-09-05
 
   INCOMPATIBLE CHANGES