Removed confusing use of unscheduled term in global exception message

The use of the term 'unscheduled' when an exception occurred during a 'global' transition was causing confusion. The term has now been dropped and the message now explicitly says it is a global transition.
Merge pull request #6027 from Dr15Jones/removeUnscheduledTermFromGlobalExceptions

Removed confusing use of unscheduled term in global exception message
Merge remote branch 'origin/CMSSW_7_3_X' into CMSSW_7_0_X