Proper open/close handling of combine stubs in combining sorter.
Combine stubs are lazily initialized upon spilling.
Adjusted combining sorter test cases.
Updated contributors.
Added cobertura Maven plugin for test coverage report generation
Added JDBC Input Formant and tests.
Fixed serialization warnings.
Marked transient fields.
Minor formattings.
Adjusted JDBC example to use internal derby DB for better debugging support.
Added DefaultInputSplitAssigner as default fallback for GenericInputSplit.
Fixed handling of unsplittable inputs and added sanity checks.
Removed redundant split generation in JDBC format after fixing unsplittabel input behavior.
Merge JobManager Webinterface
FileInputFormat builder accepts GenericDataSources.
Extended UniformPactRecordGenerator to produce keys and values starting at an offset
Extended DataSinkTask to support union input and added corresponding test case and integration test.
Remove unserializable fields in UserCodeObjectWrapper.java

This is mainly aimed at generated scala code where closures sometimes
can contain unserializable junk.

This solution is very simple. If the user code actually needs those
unserializable objects it will break at runtime with
a NullPointerException.
Change map operator to allow a map stub with open/close etc
Change duceeee operator to allow a reduce stub with open/close etc