pagination: avoid counting pages outside searches.

Replace this common pattern in controllers:

    @tags = Tag.search(search_params).paginate(params[:page], :limit => params[:limit], :search_count => params[:search])

with this:

    @tags = Tag.paginated_search(params)

`search_count` is used to skip doing a full page count when we're not
doing a search (on the assumption that the number of results will be
high when not constrained by a search). We didn't do this consistently
though. Refactor to do this in every controller.

app/controllers/users_controller.rb

@@ -29,7 +29,7 @@ class UsersController < ApplicationController
       @user = User.find_by_name!(params[:name])
       redirect_to user_path(@user)
     else
-      @users = User.search(search_params).paginate(params[:page], :limit => params[:limit], :search_count => params[:search])
+      @users = User.paginated_search(params)
       respond_with(@users)
     end
   end