Race conditions in cross-validation.

[gkronber]

Steps to reproduce:

• Create CV with Random-Forest
• Set workers to 4 and folds to 8
• Run
• The solution of the last fold ist not correctly cloned into the final ensemble combining the solutions from all folds
• (compare with only 1 worker)

[gkronber]

The event handlers for cloned algorithms in the cross validation are not thread save (iterating over cloned algorithms and checking their state). The problem occurs because in algorithm the state is set to stopped before the run is generated. In the mean-time the cross-validation also stops and collects all results, however, the last algorithm might not be finished yet.

[gkronber]

r8155: set the ExecutionState to stopped only after all results have been generated. This mitigates the problem of the race condition in CrossValidation even though the underlying problem is not actually solved.