PostgreSQL tests

I started to add tests for PostgreSQL and already fixed some issues. Though, some tests still fail. From my point of view, it is not safe to use PostgreSQL at the moment.  
``mb_strtolower($str, 'UTF-8');`` makes sense, yes. Will change it. 

>  would this match displaynames with non-lowercase characters?

exactly. this will do a case insensitive search, since *all* characters will be converted to lowercase.