If dfs.support.append is set to true AND you have put an hadoop with hadoop-4379 into hbase CLASSPATH, this patch will make it so sync use the hadoop-4379 new syncFs call.
This is a bit tough to test. You have to do messing with different hadop jars. I played around a bunch with it and it seems to do the right thing. I'll just commit since it satisfies a probably exotic need (Last time I was running 4379, namenode shutdown because of a bad generation stamp. I don't think this a 4379 issue. Its probably something that can happen if you ahve dfs.support.append=true, a bug).