Fix bug http://archives.postgresql.org/pgsql-bugs/2006-10/msg00258.php.

Fix string's length calculation for recoding, fix strlower() to avoid wrong
assumption about length of recoded string (was: recoded string is no greater
that source, it may not true for multibyte encodings)
Thanks to Thomas H. <me@alternize.com> and Magnus Hagander <mha@sollentuna.net>