"Port" the fix for issue 1974 from the trunk (2.7). Because Python 3.x does things much better, less changes are necessary.
This also shoves test_email_codecs_rename.py onto test_email_codecs.py even though the test needs to be ported to Python 3.
diff --git a/Lib/email/test/test_email.py b/Lib/email/test/test_email.py
index 8857e42..4b5065f 100644
--- a/Lib/email/test/test_email.py
+++ b/Lib/email/test/test_email.py
@@ -769,7 +769,7 @@
msg['To'] = to
eq(msg.as_string(maxheaderlen=78), '''\
To: "Someone Test #A" <someone@eecs.umich.edu>,<someone@eecs.umich.edu>,
-\t"Someone Test #B" <someone@umich.edu>,
+ "Someone Test #B" <someone@umich.edu>,
"Someone Test #C" <someone@eecs.umich.edu>,
"Someone Test #D" <someone@eecs.umich.edu>
@@ -852,7 +852,7 @@
# snug against the field name.
eq(msg.as_string(maxheaderlen=78), """\
Face-1:\x20
-\tiVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAGFBMVEUAAAAkHiJeRUIcGBi9
+ iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAGFBMVEUAAAAkHiJeRUIcGBi9
locQDQ4zJykFBAXJfWDjAAACYUlEQVR4nF2TQY/jIAyFc6lydlG5x8Nyp1Y69wj1PN2I5gzp
Face-2:\x20
iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAGFBMVEUAAAAkHiJeRUIcGBi9