Add prelim support for using linktest. Because of problems, this is
currently available to only people with stud=1 status in the DB. * www/tbauth.php3: Add a STUDLY() function to check that bit. * www/linktest.php3: New page to run linktest on the fly. The level defaults to the current level in the experiments table, but you can override that via the form on the page. * www/showexp.php3: Add link to aforementioned page. STUDLY() only. * www/beginexp_form.php3: Add an option (selection) to set the linktest level for create/swapin. Defaults to 0 (no linktest). STUDLY() only. * www/editexp.php3: Add an option to edit the default linktest level for an experiment. STUDLY() only. * tbsetup/batchexp.in and tbsetup/swapexp.in: Add code to optionally run the linktest, sending email if it fails (exists with non-zero status). Failure does not affect the swapin.