Partially implemented repack request cancellation.

objectstore/Helpers.cpp

objectstore/Helpers.hpp

scheduler/DiskReportRunner.hpp

scheduler/OStoreDB/OStoreDB.cpp

scheduler/OStoreDB/OStoreDB.hpp

scheduler/OStoreDB/OStoreDBFactory.hpp

scheduler/RepackRequest.cpp

scheduler/RepackRequest.hpp

scheduler/RepackRequestManager.hpp

scheduler/Scheduler.cpp

scheduler/Scheduler.hpp

scheduler/SchedulerDatabase.hpp

scheduler/SchedulerTest.cpp

tapeserver/daemon/MaintenanceHandler.cpp

xroot_plugins/XrdSsiCtaRequestMessage.cpp