The code below added at the begining of the .htaccess file, will redirect non-www urls to corespondent www, as expected:
# BEGIN nowww <IfModule mod_rewrite.c> RewriteEngine On RewriteBase / RewriteCond %{HTTP_HOST} !^www. RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L] </IfModule> # END nowww