*Smart Search: Illegal string offset in PHP 5.4 + tips correction

When using php 5.4 and displaying in frontend the Advanced parameters in a Smart Search form (from the menu item or from the result of a search via the module, we get 
 Warning: Illegal string offset 'class' in ROOT/libraries/cms/html/html.php on line 965

Also, the tips for the date do not display as should;

After patch, no more Warning and the tips should display like this, when hovering the Start Date or hovering the date field (if a date has been chosen when doing a second search)
![screen shot 2014-05-27 at 13 01 05](https://cloud.githubusercontent.com/assets/869724/3090571/68cec19e-e58e-11e3-90f5-9a7c0d47fb19.png)
![screen shot 2014-05-27 at 13 01 33](https://cloud.githubusercontent.com/assets/869724/3090572/6e2b0daa-e58e-11e3-9ea8-a7ab57ac38f4.png)