add useful filter handlers, exposed filters

I had a look about adding a filter handler add getting it exposed. Unfortunately it looks like the whole "exposing" feature is still TODO.

Anyway, I started adding a filter handler called "views_handler_filter_list_options" - which is targeted for "list" values like the node type. It supports multiple / not multiple value forms and different value form styles (select vs checkboxes/radios).

To get the exposed filters at least working I tried to a initial version of render_filters() for display plugins, but I failed. I just called drupal_get_form() there to get the filter form, but the problem I encountered is that the view is already built and executed at this stage. I don't know how you have planned to do this? I was also not sure how the handler forms should be separated.

I wasn't sure where I should put some things, so I just added the views_view_form() to render exposed filters/styles at the bottom of view.inc. Also I added some operator definitions views_handler_operator_eqneq() from 1.x to handlers.inc.

As I'm completely unsure how you planned to get the exposed stuff working I'm stopping here.. Hopefully it's a good start, at least views_handler_filter_list_options() should be useful.

I've used this view + hack to test the exposed node type filter:

    $view = new view;
    $view->name = 'views_node_type';
    $view->set_page_size(50);

    //display options
    $display = new views_display;
    $display->display_plugin = 'embed';
    $display->style_plugin = 'default';
    $display->id = 'embed';
    $view->display[] = $display;

    //defining the fields to display
    $field = new views_field;
    $field->tablename = 'node';
    $field->field = 'title';
    $field->display_id = 'page';
    $field->options['link_to_node'] = TRUE;
    $view->field[] = drupal_clone($field);

    $field->field = 'created';
    $view->field[] = drupal_clone($field);

    $field->tablename = 'users';
    $field->field = 'name';
    $field->options['link_to_user'] = TRUE;
    $view->field[] = $field;

    //sorting after node creation time
    $sort = new views_sort;
    $sort->tablename = 'node';
    $sort->field = 'created';
    $sort->order = 'ASC';
    $view->sort[] = $sort;

    $filter = new views_filter;
    $filter->tablename = 'node';
    $filter->field = 'type';
    $filter->operator = isset($_POST['operator']) ? $_POST['operator'] : '=';
    $filter->value = isset($_POST['value']) ? $_POST['value'] : 'page';
    $filter->exposed = 1;
    $filter->options['style'] = 'select';
    $filter->options['multiple'] = TRUE;
    $view->filter[] = $filter;

    //build, execute and render view
    $view->args = array($type);
    $view->build();
    $view->execute();
    $output .= $view->render();
    return $output;