hadoopcompatibility: Implementations of basic programming interfaces and...

... a basic driver.

* wrappers for Mapper, Reducer and Combiner (as a local Reducer) on the new Java API
* wrapper for OutputCollector
* wrappers for Partitioner, values comparator.
* a driver making it posible to run unmonitored (so far)  Hadoop jobs on Flink.
* tests and variations of the WordCount driver exclusively in Hadoop.

You can find more about the Google Summer of Code project here:  https://issues.apache.org/jira/browse/FLINK-838?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14031511
Actually, the ```IdentityReducer``` is the default reducer value by the conf for a Hadoop Job. I think we should also run it by default, as the user expects sorted data with that job.

In order to go map-only ( and no sorting) the user must set ```JobConf.setNumReduceTasks(0)```. And you are right, this must be supported properly.