Set release date for 2.6.3

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

@@ -2368,7 +2368,7 @@ Release 2.6.4 - UNRELEASED
     HADOOP-11252. RPC client does not time out by default.
     (Wilfred Spiegelenburg and Masatake Iwasaki via aajisaka)
 
-Release 2.6.3 - UNRELEASED
+Release 2.6.3 - 2015-12-17
 
   INCOMPATIBLE CHANGES
 

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

@@ -3710,7 +3710,7 @@ Release 2.6.4 - UNRELEASED
 
   BUG FIXES
 
-Release 2.6.3 - UNRELEASED
+Release 2.6.3 - 2015-12-17
 
   INCOMPATIBLE CHANGES
 

hadoop-mapreduce-project/CHANGES.txt

@@ -996,7 +996,7 @@ Release 2.6.4 - UNRELEASED
 
   BUG FIXES
 
-Release 2.6.3 - UNRELEASED
+Release 2.6.3 - 2015-12-17
 
   INCOMPATIBLE CHANGES
 

hadoop-yarn-project/CHANGES.txt

@@ -2124,7 +2124,7 @@ Release 2.6.4 - UNRELEASED
   YARN-4452. NPE when submit Unmanaged application. (Naganarasimha G R
   via junping_du)
 
-Release 2.6.3 - UNRELEASED
+Release 2.6.3 - 2015-12-17
 
   INCOMPATIBLE CHANGES