Set release date for 2.6.3

(cherry picked from commit db99e30f670cb5d73d5ec79671026eeeaf337d3d)
(cherry picked from commit 247ab92464beb55bad58b6e63eeac1a41767f432)

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

@@ -15,7 +15,7 @@ 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

@@ -24,7 +24,7 @@ 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

@@ -14,7 +14,7 @@ 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

@@ -25,7 +25,7 @@ Release 2.6.4 - UNRELEASED
     YARN-3893. Both RM in active state when Admin#transitionToActive failure 
     from refeshAll() (Bibin A Chundatt via rohithsharmaks)
 
-Release 2.6.3 - UNRELEASED
+Release 2.6.3 - 2015-12-17
 
   INCOMPATIBLE CHANGES