Add a program to recursively copy directories across file systems

A useful feature would be a simple command to copy directories recursively across filesystems. The source and destination path should be specified using a filesystem-neutral URI, such as:

hadoop cp dfs://namenode1:port1/path/to/srcdir file:///path/to/local/destination/dir

"cp" command would invoke a map-reduce program to copy files recursively.

I willl attach a patch as soon as svn is up and running.