Switch to always using dnspython (requires dnspthon>=1.12).

Also, address some documentation nits.

acme/acme/challenges.py

@@ -207,7 +207,7 @@ class KeyAuthorizationChallenge(_TokenChallenge):
 
 @ChallengeResponse.register
 class DNS01Response(KeyAuthorizationChallengeResponse):
-    """ACME "dns-01" challenge response."""
+    """ACME dns-01 challenge response."""
     typ = "dns-01"
 
     def simple_verify(self, chall, domain, account_public_key):
@@ -215,7 +215,7 @@ class DNS01Response(KeyAuthorizationChallengeResponse):
 
         :param challenges.DNS01 chall: Corresponding challenge.
         :param unicode domain: Domain name being verified.
-        :param account_public_key: Public key for the key pair
+        :param JWK account_public_key: Public key for the key pair
             being authorized.
 
         :returns: ``True`` iff validation with the TXT records resolved from a
@@ -247,7 +247,7 @@ class DNS01Response(KeyAuthorizationChallengeResponse):
 
 @Challenge.register  # pylint: disable=too-many-ancestors
 class DNS01(KeyAuthorizationChallenge):
-    """ACME "dns-01" challenge."""
+    """ACME dns-01 challenge."""
     response_cls = DNS01Response
     typ = response_cls.typ
 
@@ -298,7 +298,7 @@ class HTTP01Response(KeyAuthorizationChallengeResponse):
             being authorized.
         :param int port: Port used in the validation.
 
-        :returns: ``True`` iff validation of the files currently server by the
+        :returns: ``True`` iff validation with the files currently served by the
             HTTP server is successful.
         :rtype: bool
 

acme/acme/dns_resolver.py

@@ -25,4 +25,6 @@ def txt_records_for_name(name):
     except dns.exception.DNSException as error:
         logger.error("Error resolving %s: %s", name, str(error))
         return []
-    return [txt_rec for rdata in dns_response for txt_rec in rdata.strings]
+
+    return [txt_rec.decode("utf-8") for rdata in dns_response
+            for txt_rec in rdata.strings]

acme/setup.py

@@ -35,14 +35,10 @@ if sys.version_info < (2, 7):
 else:
     install_requires.append('mock')
 
-if sys.version_info < (3, 0):
-    dns_extras = [
-        'dnspython',
-    ]
-else:
-    dns_extras = [
-        'dnspython3',
-    ]
+# dnspython 1.12 is required to support both Python 2 and Python 3.
+dns_extras = [
+    'dnspython>=1.12',
+]
 
 dev_extras = [
     'nose',