Index::assemble searched every earlier position listed under a PostScript
name before adding the next, so an index that gives one name to many files
took time quadratic in their number. Files are visited in order, so a file
that lists a name twice can only be the last position pushed: comparing
with the end is enough.
find_postscript compared each hit's family name with every name collected
so far; it now keeps the lowercased names in a set.
Dylan M. Taylor
55332dd301