Automatically add ugoira tag to ugoira posts.

Note that this only adds the ugoira tag to .zip posts. It does not
remove the ugoira tag for posts converted from ugoira, but that aren't
true ugoira.

app/models/post.rb

@@ -562,14 +562,18 @@ class Post < ActiveRecord::Base
         tags << "huge_filesize"
       end
 
-      if file_ext == "swf"
+      if is_flash?
         tags << "flash"
       end
 
-      if file_ext == "webm"
+      if is_video?
         tags << "webm"
       end
 
+      if is_ugoira?
+        tags << "ugoira"
+      end
+
       return tags
     end