The fti.pl supplied with the fulltextindex module generate ALL possible
substrings of two characters or greater, and is case-sensitive.
This patch makes it work correctly. It generates only the suffixes of each
word, plus lowercases them - as specified by the README file.
This brings it into line with the fti.c function, makes it case-insensitive
properly, removes the problem with duplicate rows being returned from an fti
search and greatly reduces the size of the generated index table.