LJ::make_qr_link — Creates the link to toggle the QR reply form or if
LJ::make_qr_link
(dtid, basesubject, linktext, replyurl);
dtid. dtalkid for this comment
basesubject. parent comment's subject
linktext. text for the user to click
replyurl. URL to forward user to if their browser
cgi-bin/weblib.pl
undef upon failure or HTML for the link