Fix show_response behavior on Python 2

The `upload.show_response` feature was not added until Python 3. Rather
than backport it, it is now enabled only if supported.

This also adds a "smoke test" for the feature.

setuptools/command/upload.py

@@ -172,7 +172,9 @@ class upload(orig.upload):
             self.announce('Server response (%s): %s' % (status, reason),
                           log.INFO)
             if self.show_response:
-                text = self._read_pypi_response(result)
+                text = getattr(self, '_read_pypi_response',
+                               lambda x: None)(result)
+                if text is not None:
                     msg = '\n'.join(('-' * 75, text, '-' * 75))
                     self.announce(msg, log.INFO)
         else:

setuptools/tests/test_upload.py

@@ -223,3 +223,12 @@ class TestUploadTest:
         assert entries['comment'].startswith(u'built for')
         assert len(entries['comment']) > len(u'built for')
 
+    def test_show_response_no_error(self, patched_upload):
+        # This test is just that show_response doesn't throw an error
+        # It is not really important what the printed response looks like
+        # in a deprecated command, but we don't want to introduce new
+        # errors when importing this function from distutils
+
+        patched_upload.cmd.show_response = True
+        patched_upload.cmd.ensure_finalized()
+        patched_upload.cmd.run()