#2006 - Add system::mark_file_for_delete API to delete files at shutdown.
- added system::mark_file_for_delete to be called to mark a file
- added system::delete_marked_files to be called at shutdown to delete the list
- amended system::temp_filename to, by default, add the temp name to the list
- updated a few other places in code where this should be used
Merge pull request #148 from shadlaws/fix_2006

#2006 - Add system::mark_file_for_delete API to delete files at shutdown.