Looked at the hg history for changes to lines in that function.
Looks like it has always been varchar. To get some
stuff working it required the bdb engine at first.
Maybe that's why it's a varchar?

In any case at this point we should only be using innodb.

Werner, was this a "simple":

ALTER TABLE tablename_of_mutillink MODIFY linkid INTEGER;
ALTER TABLE tablename_of_mutillink MODIFY nodeid INTEGER;

followed by a call to self.create_multilink_table_indexes(spec, ml)
or maybe just a reindex for the l_idx tables at the mysql level?