Handle pre_render field handlers

There are some field handlers, which does not use the default query. They fire up a additional query.

See modules/taxonomy/views_handler_field_term_node_tid.inc as a example.

The override the query method to remove the default behavior and add a pre_render function which adds another query and stores the result in the object.

If the render method is called, it gets the result stored in the object.

So why do i tell it here: There might be stuff which is stored, but could be important for us.

This is the case also for multiple cck fields etc. I'm not sure whether this should be part of the project.