multibyte charater set in levenshtein function

Hackers,

The current version of levenshtein function in fuzzystrmatch contrib modulte
doesn't work properly with multibyte charater sets.

test=# select levenshtein('фыва','аыва');
 levenshtein
-------------
           2
(1 row)

My patch make this function works properly with multibyte charater sets.

test=# select levenshtein('фыва','аыва');
 levenshtein
-------------
           1
(1 row)

Also it avoids text_to_cstring call.

Regards,
Alexander Korotkov.