fix when pycrypto not installed

--HG--
branch : pmacs2

aesutil.py

@@ -1,9 +1,15 @@
+try:
     import Crypto.Hash.SHA256
     import Crypto.Cipher.AES
+    has_aes = True
+except:
+    has_aes = False
 
 class Crypter(object):
     ALIGNMENT = 16
     def __init__(self, password, salt='aes.py'):
+        if not has_aes:
+            raise Exception("pycrypto not installed")
         self.password = password
         self.salt     = salt
         self.hash     = Crypto.Hash.SHA256.new(password + salt)