Added support for local distributed execution environments.

Conflicts:
	stratosphere-tests/src/main/java/eu/stratosphere/test/util/AbstractTestBase.java
Fixed free memory calculation bug in case where multiple task manager run on the same jvm.
Removed local distributed executor environment from user api. Now only used for testing
Added setter and getter for numTaskManager in NepheleMiniCluster. Updated WordCountITCase and PackagedProgramEndToEndITCase accordingly.
WordCount examples are documented with many comments in order to be very user-friendly.
divided reduce and group-reduce
Add a dedicated reduce operator to be used with key extractors
Add comments to initial solution and -workset of delta iteration
Execution environment data source methods return a DataSource, to allow the setting of parameters.
Add equals and hashCode to type information.
Add test for reduce operator translation
Add test for runtime reduce drivers and fist set of fixes for stable mutable object behavior.
Remove unsafe getFieldFast() method from Tuple, because it turned out to be not faster than the switch-based getField() method.
Fix GroupReduceDriver test.
Fix ReduceDriver for mutable objects and arbitrary return types.
Fix and test reduce and Group Reduce translation for new Java API
Move PageRankITCase to proper package
Fix null pointer in ValueComparator
Add ReduceCombineDriver.
Rename CombineDriver to GroupReduceCombineDriver
Minor cleanup and fix warnings