Separate folder for each student's work in "Download all assignments as a zip"

Currently the mod/assignment provides a link to "Download all assignments as a zip", which is great except that all the students' work shows up in the same directory. Instead of using a modified filename to separate students' work it would be better (IMHO ) to put each student's work into a separate folder (named with the student's first & last name), and then keep the original file name (and extension) for each file.

This can be accomplished by changing line 1118 in mod/assignment/type/upload/assignment.class.php

$fileforzipname = clean_filename($a_user->lastname.' '. $a_user->firstname ) . "/" . clean_filename($fileoriginal . $fileext);

(this is in the download_submissions() function, in the foreach ($files as $file) loop).

I've put my changes on github at https://github.com/MikeTheGreat/moodle/tree/MDL-29343-SubfoldersForDownload (based on MOODLE_21_STABLE)

NOTE: The above change will unconditionally download as "Lastname Firstname" / "OriginalFilename.ext" - I'm not sure how to allow the user to easily choose between "Lastname Firstname" and "Firstname Lastname"