Add a section for 2.5.1 in CHANGES.txt

(cherry picked from commit dc154ab86d694e68f54c635043eb55d501d0e242)

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

@@ -318,6 +318,18 @@ Release 2.6.0 - UNRELEASED
     HADOOP-10989. Work around buggy getgrouplist() implementations on Linux that
     return 0 on failure. (cnauroth)
 
+Release 2.5.1 - UNRELEASED
+
+  INCOMPATIBLE CHANGES
+
+  NEW FEATURES
+
+  IMPROVEMENTS
+
+  OPTIMIZATIONS
+
+  BUG FIXES
+
 Release 2.5.0 - 2014-08-11
 
   INCOMPATIBLE CHANGES

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

@@ -290,6 +290,18 @@ Release 2.6.0 - UNRELEASED
 
     HDFS-4852. libhdfs documentation is out of date. (cnauroth)
 
+Release 2.5.1 - UNRELEASED
+
+  INCOMPATIBLE CHANGES
+
+  NEW FEATURES
+
+  IMPROVEMENTS
+
+  OPTIMIZATIONS
+
+  BUG FIXES
+
 Release 2.5.0 - 2014-08-11
 
   INCOMPATIBLE CHANGES

hadoop-mapreduce-project/CHANGES.txt

@@ -99,6 +99,18 @@ Release 2.6.0 - UNRELEASED
     MAPREDUCE-6044. Fully qualified intermediate done dir path breaks per-user dir
     creation on Windows. (zjshen)
 
+Release 2.5.1 - UNRELEASED
+
+  INCOMPATIBLE CHANGES
+
+  NEW FEATURES
+
+  IMPROVEMENTS
+
+  OPTIMIZATIONS
+
+  BUG FIXES
+
 Release 2.5.0 - 2014-08-11
 
   INCOMPATIBLE CHANGES

hadoop-yarn-project/CHANGES.txt

@@ -217,6 +217,18 @@ Release 2.6.0 - UNRELEASED
     YARN-2434. RM should not recover containers from previously failed attempt
     when AM restart is not enabled (Jian He via jlowe)
 
+Release 2.5.1 - UNRELEASED
+
+  INCOMPATIBLE CHANGES
+
+  NEW FEATURES
+
+  IMPROVEMENTS
+
+  OPTIMIZATIONS
+
+  BUG FIXES
+
 Release 2.5.0 - 2014-08-11
 
   INCOMPATIBLE CHANGES