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.

django/core/files/base.py

@@ -18,6 +18,10 @@ class File(FileProxyMixin):
         self.file = file
         if name is None:
             name = getattr(file, 'name', None)
+        # Use only the basename from a file's name if it's an absolute path,
+        # e.g. from NamedTemporaryFile.
+        if isinstance(name, six.string_types) and os.path.isabs(name):
+            name = os.path.basename(name)
         self.name = name
         if hasattr(file, 'mode'):
             self.mode = file.mode