When constructing an import file, we often need additional columns to construct the file that will not actually be used in the import.  e.g. if I want to import via the course_id column, while constructing, I may need to see the course title, even if I'm not using it for the import.  Because the import system insists that all columns in a file match a known title, I have to strip my title column away.  Then, if I revisit the file (to fix any errors or to reuse it), all I have are course_ids, which don't mean anything to me.  I have to then REmatch them to their course title....and then restrip the file to resubmit.    Allow a "ignore_this" or "comment_only" column header.