Remove CurrentProcessingContext from CMSSW

Remove the CurrentProcessingContext class from CMSSW
including all places where it is used, created,
updated and passed around. Uses external to the
Framework were already removed earlier. It was
mostly used in the Framework while handling exceptions.
Fix a bug related to EventSkip exception mode and
unscheduled execution. Also some minor cleanup.
Merge pull request #603 from wddgit/removeCurrentProcessingContextFromCMSSW

Remove CurrentProcessingContext from CMSSW