make sure GF2p8 is hashable..

shamirss.py

@@ -370,6 +370,9 @@ class TestShamirSS(unittest.TestCase):
 			b = GF2p8(random.randint(0, 255))
 			c = GF2p8(random.randint(0, 255))
 
+			# Hashable
+			{ a, b, c }
+
 			self.assertEqual(a * 0, 0)
 
 			# Identity