Fix UnicodeEncodeError error while reporting invalid email address.

Fixes #148.

anymail/exceptions.py

@@ -1,3 +1,5 @@
+from __future__ import unicode_literals
+
 import json
 from traceback import format_exception_only
 
@@ -40,7 +42,7 @@ class AnymailError(Exception):
 
     def __str__(self):
         parts = [
-            " ".join([str(arg) for arg in self.args]),
+            " ".join([six.text_type(arg) for arg in self.args]),
             self.describe_raised_from(),
             self.describe_send(),
             self.describe_response(),

anymail/utils.py

@@ -158,13 +158,13 @@ def parse_address_list(address_list, field=None):
     for address in parsed:
         if address.username == '' or address.domain == '':
             # Django SMTP allows username-only emails, but they're not meaningful with an ESP
-            errmsg = "Invalid email address '{problem}' parsed from '{source}'{where}.".format(
+            errmsg = u"Invalid email address '{problem}' parsed from '{source}'{where}.".format(
                 problem=address.addr_spec,
-                source=", ".join(address_list_strings),
-                where=" in `%s`" % field if field else "",
+                source=u", ".join(address_list_strings),
+                where=u" in `%s`" % field if field else "",
             )
             if len(parsed) > len(address_list):
-                errmsg += " (Maybe missing quotes around a display-name?)"
+                errmsg += u" (Maybe missing quotes around a display-name?)"
             raise AnymailInvalidAddress(errmsg)
 
     return parsed