[1.7.x] Fixed #22680 -- I/O operation on closed file.

This patch is two-fold; first it ensure that Django does close everything in
request.FILES at the end of the request and secondly the storage system should
no longer close any files during save, it's up to the caller to handle that --
or let Django close the files at the end of the request.

Backport of e2efc8965e from master.

tests/file_storage/tests.py

@@ -19,7 +19,8 @@ from django.core.cache import cache
 from django.core.exceptions import SuspiciousOperation
 from django.core.files.base import File, ContentFile
 from django.core.files.storage import FileSystemStorage, get_storage_class
-from django.core.files.uploadedfile import SimpleUploadedFile
+from django.core.files.uploadedfile import (InMemoryUploadedFile, SimpleUploadedFile,
+    TemporaryUploadedFile)
 from django.test import LiveServerTestCase, SimpleTestCase
 from django.test import override_settings
 from django.utils import six
@@ -206,6 +207,23 @@ class FileStorageTests(unittest.TestCase):
 
         self.storage.delete('path/to/test.file')
 
+    def test_save_doesnt_close(self):
+        with TemporaryUploadedFile('test', 'text/plain', 1, 'utf8') as file:
+            file.write(b'1')
+            file.seek(0)
+            self.assertFalse(file.closed)
+            self.storage.save('path/to/test.file', file)
+            self.assertFalse(file.closed)
+            self.assertFalse(file.file.closed)
+
+        file = InMemoryUploadedFile(six.StringIO('1'), '', 'test',
+                                    'text/plain', 1, 'utf8')
+        with file:
+            self.assertFalse(file.closed)
+            self.storage.save('path/to/test.file', file)
+            self.assertFalse(file.closed)
+            self.assertFalse(file.file.closed)
+
     def test_file_path(self):
         """
         File storage returns the full path of a file