Memberlist sorting case sensitive

The sorting of the fields in the memberlist is case sensitive on some of the fields.

Sorting on Username is done correctly because that sort is based on the db field 'username_clean' where case differences have been removed.

Sorting on Location (or Website) on the other hand is case sensitive making 'Oldenburg' appear before 'bristol'.

I have made a (temporary) fix by changing ...

$order_by .= $sort_key_sql[$sort_key] . ' ' . (($sort_dir == 'a') ? 'ASC' : 'DESC');

... into ...

$order_by .= 'LOWER(' . $sort_key_sql[$sort_key] . ') ' . (($sort_dir == 'a') ? 'ASC' : 'DESC');