User Import fails if there are extraneous columns in CSV [v5.5]

[dgoerger]

After repairing the CSV in #1438, User Import was still complaining, but this time was able to give an error message in the browser (in #1438 it simply failed and we needed to check the server logs). The error was that Excel had pooped out an extraneous empty column at the end, e.g.:

username,first_name,last_name,nickname,phone,email,affiliation,
netid00,test,user,,5555555555,test.user@yale.edu,Yale College,

Although the solution is obvious (don't use poorly-written office productivity software), import should probably be smart enough to handle an extraneous column.