Backport checkin:
Change decode() so that it works with a buffer (i.e. unicode(..., 'utf-8-sig'))
SF bug #1601501.
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index 62cd163..185670b 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -426,6 +426,10 @@
             ]
         )
 
+    def test_bug1601501(self):
+        # SF bug #1601501: check that the codec works with a buffer
+        unicode("\xef\xbb\xbf", "utf-8-sig")
+
 class EscapeDecodeTest(unittest.TestCase):
     def test_empty(self):
         self.assertEquals(codecs.escape_decode(""), ("", 0))