Account for SHA-256 signatures.

The test case uses OpenSSL’s default algorithm; the length 1243 corresponds to SHA-1, 1263 to SHA-256.

diff -up M2Crypto-0.21.1/tests/test_smime.py.sha256 M2Crypto-0.21.1/tests/test_smime.py
--- M2Crypto-0.21.1/tests/test_smime.py.sha256	2015-07-13 20:56:16.201862066 +0200
+++ M2Crypto-0.21.1/tests/test_smime.py	2015-07-13 20:56:30.465428800 +0200
@@ -219,7 +219,7 @@ class WriteLoadTestCase(unittest.TestCas
         buf = BIO.MemoryBuffer()
         assert SMIME.load_pkcs7(self.filename).write_der(buf) == 1
         s = buf.read()
-        assert len(s) in (1188, 1204, 1243), len(s)
+        assert len(s) in (1188, 1204, 1243, 1263), len(s)
         
     def test_load_pkcs7(self):
         assert SMIME.load_pkcs7(self.filename).type() == SMIME.PKCS7_SIGNED