Contributed by Steve Loughran.
This moves the new API of HDFS-13616 into a interface which is implemented by
HDFS RPC filesystem client (not WebHDFS or any other connector)
This new interface, BatchListingOperations, is in hadoop-common,
so applications do not need to be compiled with HDFS on the classpath.
They must cast the FS into the interface.
instanceof can probe the client for having the new interface -the patch
also adds a new path capability to probe for this.
The FileSystem implementation is cut; tests updated as appropriate.
All new interfaces/classes/constants are marked as @unstable.
Change-Id: I5623c51f2c75804f58f915dd7e60cb2cffdac681
c734d69a55