Use the normalized source in the upload form.

This makes it so you can use the bookmarklet to upload from any of these Pixiv pages:

* http://www.pixiv.net/member_illust.php?mode=medium&illust_id=45792845
* http://www.pixiv.net/member_illust.php?mode=big&illust_id=45792845
* http://www.pixiv.net/member_illust.php?mode=manga&illust_id=45792845
* http://www.pixiv.net/member_illust.php?mode=manga_big&illust_id=45792845&page=0

and the source field in the upload form will be filled in with the
actual image URL (e.g. http://i2.pixiv.net/img18/img/ringo78/45792845_big_p0.jpg),
and it will also be used for the "This post was already uploaded" check.

app/controllers/uploads_controller.rb

@@ -7,9 +7,8 @@ class UploadsController < ApplicationController
   def new
     @upload = Upload.new
     if params[:url]
-      @post = Post.find_by_source(params[:url])
-
       @normalized_url = params[:url]
+
       headers = {
         "User-Agent" => "#{Danbooru.config.safe_app_name}/#{Danbooru.config.version}"
       }
@@ -17,6 +16,8 @@ class UploadsController < ApplicationController
         @normalized_url, headers = strategy.new.rewrite(@normalized_url, headers)
       end
 
+      @post = Post.find_by_source(@normalized_url)
+
       begin
         @source = Sources::Site.new(params[:url])
       rescue Exception

app/views/uploads/new.html.erb

@@ -36,7 +36,7 @@
       <div class="input">
         <%= f.label :source %>
         <% if params[:url].present? %>
-          <%= f.text_field :source, :size => 50, :value => params[:url] %>
+          <%= f.text_field :source, :size => 50, :value => @normalized_url %>
         <% else %>
           <%= f.text_field :source, :size => 50 %>
         <% end %>