Make VCR disallow unexpected HTTP requests.

This makes it so that tests fail when they make HTTP requests they
aren't expected to. Update these tests so that they use VCR like they
should.

test/unit/upload_test.rb

@@ -104,10 +104,13 @@ class UploadTest < ActiveSupport::TestCase
         should "initialize the final path after downloading a file" do
           @upload = FactoryGirl.create(:source_upload)
           path = "#{Rails.root}/tmp/test.download.jpg"
-          assert_nothing_raised {@upload.download_from_source(path)}
-          assert(File.exists?(path))
-          assert_equal(8558, File.size(path))
-          assert_equal(path, @upload.file_path)
+
+          VCR.use_cassette("upload-test-file", :record => :once) do
+            assert_nothing_raised {@upload.download_from_source(path)}
+            assert(File.exists?(path))
+            assert_equal(8558, File.size(path))
+            assert_equal(path, @upload.file_path)
+          end
         end
       end