Release process for 2.6.1: Set the release date for 2.6.1

(cherry picked from commit 1f707ecffd80142c25ef0dee8708da49920646bc)
(cherry picked from commit f48af332a76caa89c9d8fa1d2654d290bffdc183)

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

@@ -799,7 +799,7 @@ Release 2.6.2 - UNRELEASED
 
   BUG FIXES
 
-Release 2.6.1 - 2015-09-09
+Release 2.6.1 - 2015-09-23
 
   INCOMPATIBLE CHANGES
 

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

@@ -1090,7 +1090,7 @@ Release 2.6.2 - UNRELEASED
 
   BUG FIXES
 
-Release 2.6.1 - 2015-09-09
+Release 2.6.1 - 2015-09-23
 
   INCOMPATIBLE CHANGES
 

hadoop-mapreduce-project/CHANGES.txt

@@ -271,7 +271,7 @@ Release 2.6.2 - UNRELEASED
     cache files so that child processes running hadoop scripts can access these
     files. (Junping Du via vinodkv)
 
-Release 2.6.1 - 2015-09-09
+Release 2.6.1 - 2015-09-23
 
   INCOMPATIBLE CHANGES
 

hadoop-yarn-project/CHANGES.txt

@@ -844,7 +844,7 @@ Release 2.6.2 - UNRELEASED
 
   BUG FIXES
 
-Release 2.6.1 - 2015-09-09
+Release 2.6.1 - 2015-09-23
 
   INCOMPATIBLE CHANGES