Move the change log of HADOOP-3576 into release 0.18.0 section.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.18@669601 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -1,9 +1,6 @@
 Hadoop Change Log
 
 
-    HADOOP-3576. Fix NullPointerException when renaming a directory
-    to its subdirectory. (Tse Wo (Nicholas), SZE via hairong) 
-
 Release 0.18.0 - Unreleased
 
   INCOMPATIBLE CHANGES
@@ -642,6 +639,9 @@ Release 0.18.0 - Unreleased
     HADOOP-3546. TaskTracker re-initialization gets stuck in cleaning up.
     (Amareshwari Sriramadasu via ddas)
 
+    HADOOP-3576. Fix NullPointerException when renaming a directory
+    to its subdirectory. (Tse Wo (Nicholas), SZE via hairong)
+
 Release 0.17.1 - Unreleased
 
   INCOMPATIBLE CHANGES