[1.10.x] Fixed #26644 -- Allowed wrapping NamedTemporaryFile with File.

914c72be2a introduced a regression that
causes saving a NamedTemporaryFile in a FileField to raise a
SuspiciousFileOperation. To remedy this, if a File has an absolute
path as a filename, use only the basename as the filename.

Backport of 1b407050dd from master

tests/file_storage/tests.py

@@ -10,6 +10,7 @@ import threading
 import time
 import unittest
 from datetime import datetime, timedelta
+from tempfile import NamedTemporaryFile
 
 from django.core.cache import cache
 from django.core.exceptions import SuspiciousFileOperation, SuspiciousOperation
@@ -871,6 +872,13 @@ class FileFieldStorageTests(TestCase):
         with temp_storage.open('tests/stringio') as f:
             self.assertEqual(f.read(), b'content')
 
+    def test_save_temporary_file(self):
+        storage = Storage()
+        with NamedTemporaryFile() as f:
+            f.write(b'content')
+            storage.normal = File(f)
+            storage.save()  # no crash
+
 
 # Tests for a race condition on file saving (#4948).
 # This is written in such a way that it'll always pass on platforms