[FLINK-1005] By default, new objects are created for each element in group operations
[FLINK-1214] Prevent partitionings on subsets of fields from being pushed down
Add test case for TaskManager connection loss, leading to task failure.
[FLINK-1220] Promote various log statements to INFO level. Add log statements for assignment locations
[FLINK-1222] Tasks send close acknowledgements early.
[runtime] In local mode, make sure taskmanagers have completed registration before starting a job.
[FLINK-1215] Fix spurious failures when creating output directories due to I/O races