Rendering views filters as checkboxes and radio buttons, instead of select boxes and drop down menus

This patch to the Formtweaker module, modifies views filters, so they render as checkboxes and radio buttons, instead of select boxes and drop down menus.

Currently there is no way for a user to choose between rendering a filter as checkboxes/radio buttons, or as the default select menus.

How is it done?
How do I add this condition (as a checkbox in the exposed filter section I guess) to the views ui?

(a funny note: this code started by merlinofcahos, turned into an independent module, and now comes back to his Views.module :-) )