pgsql: The attached patch implements the soundex difference function

Log Message:
-----------
The attached patch implements the soundex difference function which
compares two strings' soundex values for similarity, from Kris Jurka.
Also mark the text_soundex() function as STRICT, to avoid crashing
on NULL input.

Modified Files:
--------------
    pgsql/contrib/fuzzystrmatch:
        README.fuzzystrmatch (r1.7 -> r1.8)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/fuzzystrmatch/README.fuzzystrmatch.diff?r1=1.7&r2=1.8)
        README.soundex (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/fuzzystrmatch/README.soundex.diff?r1=1.2&r2=1.3)
        fuzzystrmatch.c (r1.14 -> r1.15)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/fuzzystrmatch/fuzzystrmatch.c.diff?r1=1.14&r2=1.15)
        fuzzystrmatch.h (r1.10 -> r1.11)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/fuzzystrmatch/fuzzystrmatch.h.diff?r1=1.10&r2=1.11)
        fuzzystrmatch.sql.in (r1.6 -> r1.7)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/fuzzystrmatch/fuzzystrmatch.sql.in.diff?r1=1.6&r2=1.7)