Add support for MD2, MD4, and MD5 to SignatureAlgorithm.

net/data/verify_certificate_chain_unittest/generate-intermediate-signed-with-md5.py

 #!/usr/bin/python
 # Copyright (c) 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Certificate chain with 1 intermediate and a trusted root. The intermediate
 however is signed using the MD5 hash. Verification is expected to fail because
 MD5 is too weak."""
 
 import common
 
 # Self-signed root certificate (used as trust anchor).
 root = common.create_self_signed_root_certificate('Root')
 
 # Intermediate.
 intermediate = common.create_intermediate_certificate('Intermediate', root)
 intermediate.set_signature_hash('md5')
 
 # Target certificate.
 target = common.create_end_entity_certificate('Target', intermediate)
 
 chain = [target, intermediate]
 trusted = common.TrustAnchor(root, constrained=False)
 time = common.DEFAULT_TIME
 verify_result = False
 errors = """[Context] Processing Certificate
   index: 0
-      [Error] Invalid or unsupported signature algorithm
-        algorithm: 300D06092A864886F70D0101040500
+      [Error] Unacceptable signature algorithm
+      [Error] VerifySignedData failed
 """
 
 common.write_test_file(__doc__, chain, trusted, time, verify_result, errors)