php forms api

I've added some field types and reviewed the field process function ( i've noticed that if a file input  was added to a fieldset, the value was not taken ).
i've also added the fields_container class ( so a fieldset is a fields_container ) and the "tabs" type fields_container.
moreover the form object is passed to the render function , so a field/fields_container can modifiy the form object ( eg. adding javascript, or attributes such as cs_file )