Updating code to run in both CHD3/4 and Hortonworks current releases

hadoop fs -ls -d is not compatible with releases other than CDH4. This update should work in all versions.
Updating code to run in both CHD3/4 and Hortonworks current releases

Updated code after the review
Cleanup in the RPC mechanism for forwards compatibility + a bunch more unit tests
Merge pull request #121 from vivshri/master

Fixing file existence check to make it compatible with various hadoop releases and distributions
Merge pull request #135 from ulzha/master

support dependency introduction through inheritance
Merge pull request #136 from erikbern/rpc-cleanup

Cleanup in the RPC mechanism for forwards compatibility + a bunch more u...
allow running without Tornado