Fix some python3 syntax errors

Milter/dns.py

@@ -26,8 +26,8 @@ def DNSLookup(name, qtype):
         # A RR as dotted quad.  For consistency, this driver should
         # return both as binary string.
         return [((a['name'], a['typename']), a['data']) for a in resp.answers]
-    except IOError, x:
-        raise DNSError, str(x)
+    except IOError as x:
+        raise DNSError(str(x))
 
 class Session(object):
   """A Session object has a simple cache with no TTL that is valid

Milter/dsn.py

@@ -142,13 +142,13 @@ def send_dsn(mailfrom,receiver,msg=None,timeout=600,session=None,ourfrom=''):
         if badrcpts:
           return badrcpts
       return None			# success
-    except smtplib.SMTPRecipientsRefused,x:
+    except smtplib.SMTPRecipientsRefused as x:
       if len(x.recipients) == 1:
         return x.recipients.values()[0]	# permanent error
       return x.recipients
-    except smtplib.SMTPSenderRefused,x:
+    except smtplib.SMTPSenderRefused as x:
       return x.args[:2]			# does not accept DSN
-    except smtplib.SMTPDataError,x:
+    except smtplib.SMTPDataError as x:
       return x.args			# permanent error
     except smtplib.SMTPException:
       pass		# any other error, try next MX