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/wiki_pages_controller.rb

@@ -16,7 +16,7 @@ class WikiPagesController < ApplicationController
   end
 
   def index
-    @wiki_pages = WikiPage.includes(:creator).search(search_params).paginate(params[:page], :limit => params[:limit], :search_count => params[:search])
+    @wiki_pages = WikiPage.includes(:creator).paginated_search(params)
     respond_with(@wiki_pages) do |format|
       format.html do
         if params[:page].nil? || params[:page].to_i == 1