Set release date for 2.6.3

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

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

@@ -857,7 +857,7 @@ 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

@@ -1193,7 +1193,7 @@ 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

@@ -315,7 +315,7 @@ 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

@@ -925,7 +925,7 @@ Release 2.6.4 - UNRELEASED
 
   BUG FIXES
 
-Release 2.6.3 - UNRELEASED
+Release 2.6.3 - 2015-12-17
 
   INCOMPATIBLE CHANGES