fix tag filtering

a story with tags [c, go] with a user's tag filter of [go] was just
removing the [go] tag from the story, not removing it from the list
completely

app/controllers/home_controller.rb

@@ -124,22 +124,26 @@ def _find_stories_for_user_and_tag_and_newest_and_by_user(user, tag = nil,
      conds.push user.id
    end

    filtered_tag_ids = []
    if user
      filtered_tag_ids = @user.tag_filters.map{|tf| tf.tag_id }
    else
      # for logged-out users, filter defaults
      filtered_tag_ids = Tag.where(:filtered_by_default => true).map{|t| t.id }
    end

    if tag
      conds[0] << "AND stories.id IN (SELECT taggings.story_id FROM " <<
        "taggings WHERE taggings.tag_id = ?)"
      conds.push tag.id
    elsif by_user
      conds[0] << "AND stories.user_id = ?"
      conds.push by_user
    elsif user
      conds[0] += " AND taggings.tag_id NOT IN (SELECT tag_id FROM " <<
        "tag_filters WHERE user_id = ?)"
      conds.push @user.id
    else
      # for logged-out users, filter defaults
      conds[0] += " AND taggings.tag_id NOT IN (SELECT id FROM " <<
        "tags WHERE filtered_by_default = ?)"
      conds.push true
    elsif filtered_tag_ids.any?
      conds[0] += " AND stories.id NOT IN (SELECT taggings.story_id " <<
        "FROM taggings WHERE taggings.tag_id IN (" <<
        filtered_tag_ids.map{|t| "?" }.join(",") << "))"
      conds += filtered_tag_ids
    end

    stories = Story.find(