Correctly redirect assets containing periods in the filename

E.g. the minister-of-funk.960x640.jpg test file.

This was causing the people.feature:57 to fail because it was being
redirected to minister-of-funk.960x640 (i.e. it was dropping the jpg
extension).

This seems to be because Rails was treating '960x640' as the extension
(previously defined in routes.rb) and 'jpg' as the format in the call to
`redirect_to`.

Renaming `extension` to `format` in routes appears to do the trick.

The change to the assets_test illustrated the problem before the change
in this commit.

TODO: Roll this into the previous commit. Without it the previous commit
fails the people.feature.

config/routes.rb

@@ -422,5 +422,5 @@ def external_redirect(path_prefix, target)
   get '/government/uploads/system/uploads/consultation_response_form/*path.:extension' => LongLifeRedirect.new('/government/uploads/system/uploads/consultation_response_form_data/')
   get '/government/uploads/system/uploads/attachment_data/file/:id/*file.:extension' => "attachments#show"
   get '/government/uploads/system/uploads/attachment_data/file/:id/*file.:extension/preview' => "attachments#preview", as: :preview_attachment
-  get '/government/uploads/*path.:extension' => "public_uploads#show", as: :public_upload
+  get '/government/uploads/*path.:format' => "public_uploads#show", as: :public_upload
 end

test/functional/public_uploads_controller_test.rb

@@ -5,7 +5,7 @@ class PublicUploadsControllerTest < ActionController::TestCase
     Plek.any_instance.stubs(:public_asset_host).returns('http://asset-host.com')
     request.host = 'not-asset-host.com'
 
-    get :show, params: { path: 'asset', extension: 'txt' }
+    get :show, params: { path: 'asset', format: 'txt' }
 
     assert_redirected_to 'http://asset-host.com/government/uploads/asset.txt'
   end
@@ -17,7 +17,7 @@ class PublicUploadsControllerTest < ActionController::TestCase
     Plek.any_instance.stubs(:public_asset_host).returns('http://asset-host.com')
     request.host = 'asset-host.com'
 
-    get :show, params: { path: 'asset', extension: 'txt' }
+    get :show, params: { path: 'asset', format: 'txt' }
 
     assert_response 200
   end

test/integration/assets_test.rb

@@ -2,7 +2,7 @@
 
 class AssetsTest < ActionDispatch::IntegrationTest
   setup do
-    asset_filename = 'asset.txt'
+    asset_filename = 'asset.tmp.txt'
     @asset_filesystem_path = File.join(Whitehall.clean_uploads_root, asset_filename)
     FileUtils.touch(@asset_filesystem_path)