Improve compatibility warning about HBase with Hadoop 0.23.x

Hmaster is not able to start because of the following error
Please find the following error
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2012-03-30 11:12:19,487 FATAL org.apache.hadoop.hbase.master.HMaster: Unhandled exception. Starting shutdown.
java.lang.NoClassDefFoundError: org/apache/hadoop/hdfs/protocol/FSConstants$SafeModeAction
at org.apache.hadoop.hbase.util.FSUtils.waitOnSafeMode(FSUtils.java:524)
at org.apache.hadoop.hbase.master.MasterFileSystem.checkRootDir(MasterFileSystem.java:324)
at org.apache.hadoop.hbase.master.MasterFileSystem.createInitialFileSystemLayout(MasterFileSystem.java:127)
at org.apache.hadoop.hbase.master.MasterFileSystem.<init>(MasterFileSystem.java:112)
at org.apache.hadoop.hbase.master.HMaster.finishInitialization(HMaster.java:496)
at org.apache.hadoop.hbase.master.HMaster.run(HMaster.java:363)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.hdfs.protocol.FSConstants$SafeModeAction
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
... 7 more
There is a change in the FSConstants