Unittest for ClassCastException if exception happens when Collator is set to mapreduce job
Fixed ClassCastException in mapreduce framework if exception is thrown but collator is set
Fixed exception propagation
Added try/catch to collate operation because it is not running on caller thread and exception might get lost otherwise
Made better exception handling for remote operation exceptions
Unittest for NotSerializableException if you want to use DataSerializable for intermediate values on mapreduce jobs
Fixed serialization problem when maps are used to transfer DataSerializable objects
Fixed expected values for unittest
Added unittest for null results from combiner chunks
Fixed sending of non used values (combiner side) for this chunk - resulting in null values for a key
Fixed checkstyle errors
Fixed disappeared fail import
Removed reflective access
Merge pull request #2553 from noctarius/mapreduce-bugfixes-maintenance

Mapreduce bugfixes Backport