Set build version to 0.21.0

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.21@939920 13f79535-47bb-0310-9956-ffa450edef68

build.xml

@@ -28,7 +28,7 @@
  
   <property name="Name" value="Hadoop-core"/>
   <property name="name" value="hadoop-core"/>
-  <property name="version" value="0.22.0-SNAPSHOT"/>
+  <property name="version" value="0.21.0-SNAPSHOT"/>
   <property name="final.name" value="${name}-${version}"/>
   <property name="test.final.name" value="${name}-test-${version}"/>
   <property name="year" value="2009"/>