Made Python Crypto lib become a soft dependency.

scapy/all.py

@@ -40,4 +40,4 @@ from asn1.asn1 import *
 from asn1.ber import *
 from asn1.mib import *
 
-from crypto.cert import *
+from crypto import *

scapy/crypto/__init__.py

@@ -3,4 +3,13 @@
 ## Copyright (C) Arnaud Ebalard <arno@natisbad.org>
 ## This program is published under a GPLv2 license
 
-__all__ = ["cert"]
+
+
+try:
+    import Crypto
+except ImportError:
+    import logging
+    log_loading = logging.getLogger("scapy.loading")
+    log_loading.info("Can't import python Crypto lib. Disabled certificate manipulation tools")
+else:
+    from scapy.crypto.cert import *