Fixed #27658 -- Prevented collectstatic from overwriting newer files in remote storages.

Thanks revimi for the initial patch.

tests/staticfiles_tests/storage.py

@@ -1,6 +1,6 @@
 import errno
 import os
-from datetime import datetime
+from datetime import datetime, timedelta
 
 from django.conf import settings
 from django.contrib.staticfiles.storage import CachedStaticFilesStorage
@@ -59,6 +59,14 @@ class PathNotImplementedStorage(storage.Storage):
         raise NotImplementedError
 
 
+class NeverCopyRemoteStorage(PathNotImplementedStorage):
+    """
+    Return a future modified time for all files so that nothing is collected.
+    """
+    def get_modified_time(self, name):
+        return datetime.now() + timedelta(days=30)
+
+
 class QueryStringStorage(storage.Storage):
     def url(self, path):
         return path + '?a=b&c=d'