mysqldump dbname > dbname_bak_before_messing_with_it.sql
mysqldump --default-character-set=latin1 --skip-set-charset dbname > dump.sql
sed -r 's/latin1/utf8/g' dump.sql > dump_utf.sql
mysql --execute="DROP DATABASE dbname; CREATE DATABASE dbname CHARACTER SET utf8 COLLATE utf8_general_ci;" 
mysql --default-character-set=utf8 dbname < dump_utf.sql