Add extraction of upload extension. Add rspec test for search of post

with upload by extension.

lib/upload_creator.rb

@@ -73,6 +73,7 @@ class UploadCreator
       @upload.sha1              = sha1
       @upload.url               = ""
       @upload.origin            = @opts[:origin][0...1000] if @opts[:origin]
+      @upload.extension         = File.extname(@filename)[1..10]
 
       if FileHelper.is_image?(@filename)
         @upload.width, @upload.height = ImageSizer.resize(*@image_info.size)