python3 fix + arc cmd tool fix

ChangeLog

@@ -1,4 +1,5 @@
 UNRELEASED Version 0.6.1
+    - Fixed python3 dns lookup issue
 
 2017-01-23 Version 0.6.0
     - Add capability to sign and verify ARC signatures

arcverify.py

@@ -40,10 +40,10 @@ message = sys.stdin.read()
 verbose = '-v' in sys.argv
 if verbose:
   logging.basicConfig(level=10)
-  d = dkim.ARC(message)
+  a = dkim.ARC(message)
-  cv, results, comment = d.verify()
+  cv, results, comment = a.verify()
 else:
-  cv, results, comment = arc.verify(message)
+  cv, results, comment = dkim.arc_verify(message)
 
 print("arc verification: cv=%s %s" % (cv, comment))
 if verbose:

dkim/dnsplug.py

@@ -80,6 +80,6 @@ def get_txt(name):
     except UnicodeDecodeError:
         return None
     txt = _get_txt(unicode_name)
-    if txt:
+    if type(txt) is str:
       txt = txt.encode('utf-8')
     return txt