fix can_sign: detect if OldWallet is used

lib/wallet.py

@@ -1048,9 +1048,11 @@ class Abstract_Wallet(object):
             addr = bitcoin.public_key_to_bc_address(x_pubkey.decode('hex'))
             return self.is_mine(addr)
         elif x_pubkey[0:2] == 'ff':
+            if isinstance(self, OldWallet): return False
             xpub, sequence = BIP32_Account.parse_xpubkey(x_pubkey)
             return xpub in [ self.master_public_keys[k] for k in self.master_private_keys.keys() ]
         elif x_pubkey[0:2] == 'fe':
+            if not isinstance(self, OldWallet): return False
             xpub, sequence = OldAccount.parse_xpubkey(x_pubkey)
             return xpub == self.get_master_public_key()
         elif x_pubkey[0:2] == 'fd':