Simpler and earlier validation for D6

I was having problems logging in (registration seemed OK). So I simplified/updated the code a bit. We now register an #element_validate handler on the name element since those run before form-wide validation. We want to run early so the login form looks as "normal" as possible as it proceeds through validation. I also changed from form_set_value() to just setting $form_state['values']['name'] since thats clearer and supported in D6.