Pass on cancel event to the window shutdown handler
Merge pull request #3101 from DynamoDS/master_shutdownCancelFix

Pass on cancel event to the window shutdown handler
Merge branch 'master' of https://github.com/DynamoDS/Dynamo into Revit2015
Merge branch 'Revit2015' of https://github.com/DynamoDS/Dynamo into RC0.7.4_Revit2015